U.S. patent application number 09/784181 was filed with the patent office on 2001-08-23 for semiconductor memory device and method for setting stress voltage.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Kato, Yoshiharu, Kawamoto, Satoru.
Application Number | 20010015926 09/784181 |
Document ID | / |
Family ID | 18564833 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015926 |
Kind Code |
A1 |
Kato, Yoshiharu ; et
al. |
August 23, 2001 |
Semiconductor memory device and method for setting stress
voltage
Abstract
The present invention provides a semiconductor memory device
that performs a burn-in test. The device includes word lines, pairs
of bit lines, memory cells, sense amplifiers connected to the pairs
of bit lines for amplifying a potential difference between the
associated pair of bit lines, and a burn-in test control circuit
for providing a stress voltage to the plurality of word lines and
the pairs of bit lines to perform a burn-in test based on the
burn-in control signal. The burn-in test control circuit includes a
potential difference setting circuit for selecting one of the first
word lines so to generate a potential difference between at least
one of the pairs of bit lines. The sense amplifiers amplify the
potential difference to provide the stress voltage between the word
lines and the associated pair of bit lines and between the bit
lines of that pair.
Inventors: |
Kato, Yoshiharu;
(Kasugai-shi, JP) ; Kawamoto, Satoru;
(Kasugai-shi, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
FUJITSU LIMITED
|
Family ID: |
18564833 |
Appl. No.: |
09/784181 |
Filed: |
February 16, 2001 |
Current U.S.
Class: |
365/201 |
Current CPC
Class: |
G11C 11/401 20130101;
G11C 29/50 20130101 |
Class at
Publication: |
365/201 |
International
Class: |
G11C 029/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 18, 2000 |
JP |
2000-041622 |
Claims
What is claimed is:
1. A semiconductor memory device comprising: a plurality of word
lines including first word lines; pairs of bit lines intersecting
the plurality of word lines; a plurality of memory cells located at
the intersections between the plurality of word lines and the pairs
of bit lines; a plurality of sense amplifiers, each connected to
one of the pairs of bit lines for amplifying a potential difference
between the associated pair of bit lines; and a burn-in test
control circuit for providing a stress voltage to the plurality of
word lines and the pairs of bit lines to perform a burn-in test
based on a burn-in control signal, wherein the burn-in test control
circuit includes a potential difference setting circuit for
selecting at least one of the first word lines before selection of
the plurality of word lines to generate a potential difference
between at least one of the pairs of bit lines based on the burn-in
control signal, and wherein each of the sense amplifiers amplifies
the potential difference to provide the stress voltage between the
plurality of word lines and the associated pair of bit lines and
between the associated pair of bit lines.
2. The semiconductor memory device according to claim 1 further
comprising: a dummy cell connected to each intersection between the
first word lines and the bit lines, wherein the first word lines
are dummy word lines, and wherein the potential difference setting
circuit includes the dummy words lines, the dummy cells, and a
dummy word control circuit for selecting at least one of the dummy
word lines before selection of the plurality of word lines to
generate a potential difference corresponding to the dummy cells
between the at least one of the pairs of bit lines based on the
burn-in control signal.
3. The semiconductor memory device according to claim 2, further
comprising: a word decoder driver connected to the plurality of
word lines for selecting at least one of the plurality of word
lines, wherein the word decoder driver includes a predecoder for
simultaneously selecting all of the plurality of word lines based
on the burn-in control signal.
4. The semiconductor memory device according to claim 2, wherein
the dummy word control circuit selects one of the dummy word lines
based on a selection signal.
5. The semiconductor memory device according to claim 2, wherein
the memory cells each include a capacitor, and the dummy cells
comprise coupling capacitors, and wherein each of the coupling
capacitors has a capacitance smaller than that of the capacitor of
one of the memory cells.
6. The semiconductor memory device according to claim 2, wherein
the memory cells each include a capacitor, and the dummy cells each
include a transistor and a capacitor, and wherein the capacitor of
one of the dummy cells has a capacitance smaller than that of the
capacitor of one of the memory cells.
7. The semiconductor memory device according to claim 1, further
comprising a word decoder driver for selecting at least one of the
plurality of word lines, wherein the word decoder driver includes a
predecoder for simultaneously selecting all of the plurality of
word lines based on the burn-in control signal.
8. A semiconductor memory device comprising: a plurality of words
lines; pairs of bit lines intersecting the word lines; a plurality
of memory cells located at the intersections between the word lines
and the pairs of bit lines; a plurality of sense amplifiers, each
connected to one of the pairs of bit lines for amplifying a
potential difference between the associated pair of bit lines; a
plurality of column gates, each connected to one of the pairs of
bit lines; a plurality of data buses connected via the column gates
to the pairs of bit lines; and a burn-in test control circuit for
providing a stress voltage to the word lines and the pairs of bit
lines so to perform a burn-in test based on a burn-in control
signal, wherein the burn-in test control circuit includes: a
potential generation circuit connected to the plurality of data
buses for generating a potential difference between the plurality
of data buses based on the burn-in control signal; and a column
decoder connected to the column gates to connect the plurality of
data buses to the pairs of bit lines based on the burn-in control
signal, wherein each of the sense amplifiers amplifies the
potential difference to provide the stress voltage between the
plurality of word lines and the associated pair of bit lines and
between the associated pair of bit lines.
9. The semiconductor memory device according to claim 8, wherein
the plurality of data buses include a pair of local data buses
connected to the plurality of bit lines and a pair of global data
buses connected to the pair of local data buses, and wherein the
potential generation circuit is connected to each of the pair of
local data buses.
10. The semiconductor memory device according to claim 9, wherein
the potential generation circuit selectively provides a first
potential and a second potential to the pair of local data buses
based on a selection signal.
11. The semiconductor memory device according to claim 8, wherein
the plurality of data buses include a pair of local data buses
connected to the plurality of bit lines and a pair of global data
buses connected to the pair of local data buses, wherein the
potential generation circuit is connected to the pair of global
data buses.
12. The semiconductor memory device according to claim 11, wherein
the potential generation circuit selectively provides a first
potential and a second potential to the pair of global data buses
based on a selection signal.
13. The semiconductor memory device according to claim 9, wherein
the potential generation circuit is a local equalizer for providing
a precharge voltage to one of the pair of local data buses based on
the burn-in control signal.
14. The semiconductor memory device according to claim 11, wherein
the potential generation circuit is a global equalizer for
providing a precharge voltage to one of the pair of global data
buses based on the burn-in control signal.
15. A semiconductor memory device comprising: a plurality of words
lines; pairs of bit lines intersecting the word lines; a plurality
of memory cells located at the intersections between the word lines
and the pairs of bit lines; a plurality of sense amplifiers, each
connected to one of the pairs of bit lines for amplifying a
potential difference between the associated pair of bit lines,
wherein each of the sense amplifiers includes a pair of input
nodes; plural sets of bit line separation switches, each connected
between the associated pair of bit lines and the pair of input
nodes of the associated sense amplifier; and a burn-in test control
circuit for providing a stress voltage to the plurality of word
lines and the pairs of bit lines to perform a burn-in test based on
a burn-in control signal, wherein the burn-in test control circuit
includes a switch control circuit for selectively activating one
set of the bit line separation switches associated with one of the
pairs of bit lines based on the burn-in control signal before
selection of the word lines, so to produce a potential difference
between the input nodes of the sense amplifier associated with the
set of the bit line separation switches.
16. The semiconductor memory device according to claim 15, wherein
the switch control circuit selectively activates the one set of the
bit line separation switches based on a switch selection signal and
selectively provides a first potential and a second potential to
the pair of input nodes.
17. A method for setting a stress voltage applied to a
semiconductor memory device, wherein the semiconductor memory
device includes a plurality of word lines, pairs of bit lines
intersecting the word lines, a plurality of dummy word lines
intersecting the pairs of bit lines, and a plurality of sense
amplifiers each connected to one of the pairs of bit lines for
amplifying a potential difference between the associated pair of
bit lines, the method comprising the steps of: selecting at least
one of the dummy word lines; producing a potential difference
between at least one of the pairs of bit lines; amplifying the
potential difference by activating the sense amplifier associated
with the at least one of the pairs of bit lines; selecting all of
the word lines; and providing a stress voltage between all of the
word lines and the at least one of the pairs of bit lines and
between the at least one of the pairs of bit lines.
18. A method for setting a stress voltage applied to a
semiconductor memory device, wherein the semiconductor memory
device includes a plurality of word lines, pairs of bit lines
intersecting the word lines, a plurality of dummy word lines
intersecting the pairs of bit lines, a plurality of sense
amplifiers each connected to one of the pairs of bit lines for
amplifying a potential difference between the associated pair of
bit lines, and a pair of data buses connected via the column gates
to the pairs of bit lines, the method comprising the steps of:
generating a potential difference between the pair of data buses;
providing the potential difference to the pairs of bit lines by
connecting the pair of data buses to the pairs of bit lines;
amplifying the potential difference by activating the sense
amplifiers; selecting all of the word lines; and providing a stress
voltage between all of the word lines and the pairs of bit lines
and between the pairs of bit lines.
19. A method for setting a stress voltage applied to a
semiconductor memory device, wherein the semiconductor memory
device includes a plurality of word lines, pairs of bit lines
intersecting the word lines, a plurality of dummy word lines
intersecting the pairs of bit lines, a plurality of sense
amplifiers each having a pair of input nodes and connected to one
of the pairs of bit lines for amplifying a potential difference
between the associated pair of bit lines, and plural sets of bit
line separation switches each connected to one of the pairs of bit
lines and to the pair of input nodes of the associated sense
amplifier, the method comprising: activating one set of the bit
line separation switches associated with one of the pairs of bit
lines to produce a potential difference between the pair of the
input nodes of the sense amplifier associated with the one set of
the bit line separation switches; selecting all of the word lines;
amplifying the potential difference by activating the sense
amplifier associated with the one set of the bit line separation
switches; and providing a stress voltage between all of the word
lines and one of the pairs of bit lines and between the pairs of
bit lines by activating the one set of the bit line separation
switches.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a semiconductor memory
device. More particularly, it relates to a semiconductor memory
device provided with a burn-in test function.
[0002] In the prior art, word lines and bit lines that are
connected to a memory cell in a semiconductor memory device undergo
a burn-in test. The burn-in test is performed during a final
testing process, which is performed after a packaging process.
Further, the burn-in test takes a long time since the word lines
must be sequentially accessed. However, contemporary semiconductor
memory devices are often delivered to a user's plant, which are
still in the form of chips before undergoing the packaging process.
Consequently, the burn-in test is normally performed during a wafer
testing process.
[0003] In a memory device, such as a DRAM, word lines are selected
one at a time in normal operation, during which information is read
from or written to memory cells. Then, among the memory cells
connected to the selected word lines, information is read from or
written to the memory cell that is connected to a selected
column.
[0004] When performing the burn-in test during the wafer testing
process, multiple word lines and bit lines are simultaneously
selected, and a stress voltage is applied between the word lines
and bit lines or between the bit lines for a predetermined time to
shorten the burn-in test time.
[0005] Accordingly, in addition to circuits for performing normal
operations, a memory device having a burn-in test function must
incorporate a circuit for performing the burn-in test. A large
number of such burn-in test circuits has been proposed.
[0006] For example, Japanese Unexamined Patent Publication No.
10-340598 describes a switch circuit that provides a stress voltage
to each bit line from an external device based on a test mode
detection signal when performing the burn-in test. Japanese
Unexamined Patent Publication No. 4-232693 also describes a switch
circuit having a similar function.
[0007] These burn-in test circuits require a switch circuit for
each bit line and a control signal line for each switch circuit.
Thus, a burn-in circuit as described significantly increases the
circuit area of the memory device.
[0008] Japanese Unexamined Patent Publication 11-86597 describes a
test circuit that includes a switch circuit connected to each bit
line to control the potential at the bit line. When performing the
burn-in test, one of the switch circuits connected to a pair of the
bit lines is activated to produce a potential difference between
the pair of the bit lines. A sense amplifier is then activated to
provide a stress voltage to each bit line.
[0009] The above burn-in test circuit also requires a switch
circuit for each bit line and a control signal line for each switch
circuit. Thus, this burn-in test circuit, too, significantly
increases the circuit area of the memory device.
[0010] Japanese Unexamined Patent Publication 10-92197 describes a
test circuit that activates a sense amplifier with a burn-in
control signal. This causes the sense amplifier to provide a stress
voltage to each bit line. Although a switch circuit is not required
for each bit line in this burn-in test circuit, the operation of
the sense amplifier makes it difficult to control the stress
voltage provided to a pair of bit lines. In other words, the
potential at each bit line when the sense amplifier is activated
determines which one of the bit lines takes a high potential.
Therefore, although short-circuits between a pair of bit lines are
screened, short-circuits between bit lines of adjacent columns may
not be screened. As a result, the burn-in test reduces the
screening reliability.
[0011] Japanese Unexamined Patent Publication No. 6-223595
describes a test circuit that selects every write decoder and
provides a stress voltage from a write amplifier to each bit line
during a burn-in test.
[0012] Further, Japanese Unexamined Patent Publication No. 11-86597
describes a test circuit that provides a stress voltage from I/O
circuits to the bit lines. Cell information is provided by the
input and output through the I/O circuits, when the cell
information is transferred between a data bus and columns.
[0013] The circuit area of cell arrays does not have to be
increased in these test circuits since the decoders or I/O
circuits, which are used during normal read and write operations,
are employed to provide the stress voltage. During the burn-in
test, however, every one of the bit lines applies a load to the
write amplifier, which provides the stress voltage to the bit lines
during the burn-in test. Thus, the load applied to the write
amplifier is increased. This may cause an insufficient stress
voltage being provided to the bit lines during the burn-in test and
consequently decrease the screening reliability.
[0014] In addition, since all of the write decoders or I/O circuits
are selected, the number of inputs of each decoder must increase,
for example, from three to four. If the increase in the number of
inputs occurs in many decoders, the number of logic gates will
increase significantly. And the circuit area of peripheral circuits
in a cell array will also increase.
[0015] As such, although many memory devices equipped with a
burn-in test function have been proposed, the circuit area of cell
arrays is increased when a switch circuit is connected to each bit
line to ensure the supply of a stress voltage to each bit line.
[0016] Further, when a stress voltage is provided to each bit line
without increasing the circuit area of cell arrays, the circuit
area of peripheral circuits increases and each bit line does not
acquire a sufficient stress voltage.
SUMMARY OF THE INVENTION
[0017] It is an object of the present invention to provide a
semiconductor memory device equipped with a burn-in test function
that ensures the screening of early failures without increasing the
circuit area.
[0018] To achieve the above object, the present invention provides
a semiconductor memory device including a plurality of word lines
having first word lines, pairs of bit lines intersecting the
plurality of word lines, a plurality of memory cells located at the
intersections between the plurality of word lines and the pairs of
bit lines, a plurality of sense amplifiers each connected to one of
the pairs of bit lines for amplifying a potential difference
between the associated pair of bit lines, and a burn-in test
control circuit for providing a stress voltage to the plurality of
word lines and the pairs of bit lines to perform a burn-in test
based on a burn-in control signal. The burn-in test control circuit
includes a potential difference setting circuit for selecting at
least one of the first word lines before selection of the plurality
of word lines to generate a potential difference between at least
one of the pairs of bit lines based on the burn-in control signal.
Each of the sense amplifiers amplifies the potential difference to
provide the stress voltage between the plurality of word lines and
the associated pair of bit lines and between the associated pair of
bit lines.
[0019] The present invention also provides a semiconductor memory
device including a plurality of words lines, pairs of bit lines
intersecting the word lines, a plurality of memory cells located at
the intersections between the word lines and the pairs of bit
lines, a plurality of sense amplifiers each connected to one of the
pairs of bit lines for amplifying a potential difference between
the associated pair of bit lines, a plurality of column gates each
connected to one of the pairs of bit lines, a pair of data buses
connected via the column gates to the pairs of bit lines, and a
burn-in test control circuit for providing a stress voltage to the
word lines and the pairs of bit lines to perform a burn-in test
based on the burn-in control signal. The burn-in test control
circuit includes a potential generation circuit connected to the
pair of data buses for generating a potential difference between
the data buses based on the burn-in control signal, and a column
decoder connected to the column gates to connect the pair of data
buses to the pairs of bit lines based on the burn-in control
signal. Each of the sense amplifiers amplifies the potential
difference to provide the stress voltage between the plurality of
word lines and the associated pair of bit lines and between the
associated pair of bit lines.
[0020] The present invention further provides a semiconductor
memory device including a plurality of words lines, pairs of bit
lines intersecting the word lines, a plurality of memory cells
located at the intersections between the word lines and the pairs
of bit lines, and a plurality of sense amplifiers each connected to
one of the pairs of bit lines for amplifying a potential difference
between the associated pair of bit lines. Each of the sense
amplifiers includes a pair of input nodes. Plural sets of bit line
separation switches are each connected between the associated pair
of bit lines and the pair of input nodes of the associated sense
amplifier. A burn-in test control circuit provides a stress voltage
to the word lines and the pairs of bit lines to perform a burn-in
test based on a burn-in control signal. The burn-in test control
circuit includes a switch control circuit for activating one of the
bit line separation switches associated with one of the pairs of
bit lines based on the burn-in control signal, before selecting the
word lines to produce a potential difference between the input
nodes of the sense amplifier associated with one set of the bit
line separation switches.
[0021] The present invention further provides a method for setting
a stress voltage applied to a semiconductor memory device. The
semiconductor memory device includes a plurality of word lines,
pairs of bit lines intersecting the word lines, a plurality of
dummy word lines intersecting the pairs of bit lines, and a
plurality of sense amplifiers each connected to one of the pairs of
bit lines for amplifying a potential difference between the
associated pair of bit lines. The method includes selecting at
least one of the dummy word lines, producing a potential difference
between at least one of the pairs of bit lines, amplifying the
potential difference by activating the sense amplifier associated
with the at least one of the pairs of bit lines, selecting all of
the word lines, and providing a stress voltage between all of the
word lines and the at least one of the pairs of bit lines and
between the at least one of the pairs of bit lines.
[0022] The present invention further provides a method for setting
a stress voltage applied to a semiconductor memory device. The
semiconductor memory device includes a plurality of word lines,
pairs of bit lines intersecting the word lines, a plurality of
dummy word lines intersecting the pairs of bit lines, a plurality
of sense amplifiers each connected to one of the pairs of bit lines
for amplifying a potential difference between the associated pair
of bit lines, and a pair of data buses connected via the column
gates to the pairs of bit lines. The method includes generating a
potential difference between the pair of data buses, providing the
potential difference to the pairs of bit lines by connecting the
pair of data buses to the pairs of bit lines, amplifying the
potential difference by activating the sense amplifiers, selecting
all of the word lines, and providing a stress voltage between all
of the word lines and the pairs of bit lines and between the pairs
of bit lines.
[0023] The present invention further provides a method for setting
a stress voltage applied to a semiconductor memory device. The
semiconductor memory device includes a plurality of word lines,
pairs of bit lines intersecting the word lines, a plurality of
dummy word lines intersecting the pairs of bit lines, a plurality
of sense amplifiers each having a pair of input nodes and connected
to one of the pairs of bit lines for amplifying a potential
difference between the associated pair of bit lines, and plural
sets of bit line separation switches each connected to one of the
pairs of bit lines and to the pair of input nodes of the associated
sense amplifier. The method includes activating one set of the bit
line separation switches associated with one of the pairs of bit
lines to produce a potential difference between the pairs of the
input nodes of the sense amplifier associated with the one set of
the bit line separation switches, selecting all of the word lines,
amplifying the potential difference by activating the sense
amplifier associated with the one set of the bit line separation
switches, and providing a stress voltage between all of the word
lines and one of the pairs of bit lines and between the pairs of
bit lines by activating the one set of the bit line separation
switches.
[0024] Other aspects and advantages of the present invention will
become apparent from the following description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention, together with objects and advantages thereof,
may be best understood by reference to the description of the
following exemplary embodiments together with the accompanying
drawings in which:
[0026] FIG. 1 is a schematic block circuit diagram of a
semiconductor memory device according to a first embodiment of the
present invention;
[0027] FIG. 2 is a schematic circuit diagram of a section of a
memory cell array in the semiconductor memory device of FIG. 1;
[0028] FIG. 3 is a circuit diagram of an exemplary dummy cell in
the memory cell array of FIG. 2;
[0029] FIG. 4 is a schematic circuit diagram of a word control
circuit in the semiconductor memory device of FIG. 1;
[0030] FIG. 5 is a schematic circuit diagram of a dummy word
control circuit in the semiconductor memory device of FIG. 1;
[0031] FIG. 6 is a schematic circuit diagram of a dummy word
decoder and a driver in the semiconductor memory device of FIG.
1;
[0032] FIG. 7 is a schematic circuit diagram of a sense amplifier
control circuit in the semiconductor memory device of FIG. 1;
[0033] FIG. 8 is a schematic circuit diagram of a word decoder and
a driver in the semiconductor memory device of FIG. 1;
[0034] FIG. 9 is a combined timing and waveform chart illustrating
the operation of the semiconductor memory device of FIG. 1 during a
burn-in test;
[0035] FIG. 10 is a combined timing and waveform chart illustrating
the operation of the semiconductor memory device of FIG. 1 during a
normal read operation;
[0036] FIG. 11 is a schematic block circuit diagram of a
semiconductor memory device according to a second embodiment of the
present invention;
[0037] FIG. 12 is a schematic block circuit diagram of a
semiconductor memory device according to a third embodiment of the
present invention;
[0038] FIG. 13 is a schematic block circuit diagram of a section of
a memory array in a semiconductor memory device according to a
fourth embodiment of the present invention;
[0039] FIG. 14 is a circuit diagram of a first control circuit for
controlling the memory array of FIG. 13;
[0040] FIG. 15 is a circuit diagram of a second control circuit for
controlling the memory array of FIG. 13;
[0041] FIG. 16 is a combined timing and waveform chart illustrating
the operation of the semiconductor memory device of FIG. 13 during
a normal read operation;
[0042] FIG. 17 is a combined timing and waveform chart illustrating
the operation of the semiconductor memory device of FIG. 13 during
a burn-in test; and
[0043] FIG. 18 is a schematic block circuit diagram of a section of
a memory array in a semiconductor memory device according to a
fifth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] In the drawings, like numerals are used for like elements
throughout.
[0045] [First Embodiment]
[0046] FIG. 1 is a schematic block circuit diagram of a
semiconductor memory device 100 according to a first embodiment of
the present invention. FIG. 2 is a schematic circuit diagram
showing a section of a memory cell array 1 of the semiconductor
memory device 100.
[0047] The memory cell array 1 includes word lines WL0-WLn and
pairs of bit lines BLZ, BLX. With reference to FIG. 2, among the
word lines WL0-WLn, for example, Memory cells MC are connected
respectively between the even word lines and the bit lines BLZ and
between the odd word lines and the bit lines BLX.
[0048] The word lines WL0-WLn are connected to a word decoder
driver 2. During normal read and write operations, the word decoder
driver 2 receives an address signal Add and accordingly selects one
of the word lines.
[0049] The memory cell array 1 also includes two dummy word lines
DWL0, DWL1. Dummy cells DMC are connected respectively between the
dummy word line DWL0 and the bit line BLZ and between the dummy
word line DWL1 and the bit line BLX. Each dummy cell DMC is
provided by a coupling capacitor. As shown in FIG. 3, a dummy cell
DMC may be alternatively provided by a cell transistor 4 and a cell
capacitor 5. In this case, the size of the cell capacitor 5 is one
half the size of the cell capacitor in a memory cell MC.
[0050] Referring back to FIG. 1, the dummy word lines DWL0, DWL1
are connected to a dummy word decoder driver 3. During normal
operation, the dummy word decoder driver 3 receives the address
signal Add. The dummy word decoder driver 3, for example, selects
the dummy word line DWL1 when an even word line is selected and
selects the dummy word line DWL0 when an odd word line is
selected.
[0051] As described in Japanese Unexamined Patent Publication Nos.
7-201199 and 6-84348, one of the dummy word lines DWL0, DWL1 is
selected in accordance with the selected word line among the word
lines WL0-WLn. The coupling capacitance between the selected dummy
word line and bit line increases the potential difference between
the pair of bit lines from which cell information is read. This
stabilizes the read operation and obtains a margin for refresh
operations.
[0052] A sense amplifier 6 is connected between each pair of the
bit lines BLZ, BLX. Each sense amplifier 6 is activated by sense
amplifier voltages PSA, NSA supplied by a sense amplifier control
circuit 7, and further amplifies the potential difference between
the associated pair of bit lines BLZ, BLX.
[0053] A word control circuit 8, which controls the selection of
the word lines WL0-WLn, receives a master clock signal CLK from an
external device (not shown) and a burn-in control signal BIZ during
a burn-in test. The word control circuit 8 provides a first clock
signal CLK1 to the word decoder driver 2, and a second clock signal
CLK2 to the dummy word control circuit 9 and to the sense amplifier
control circuit 7.
[0054] The word decoder driver 2 is also provided with the burn-in
control signal BIZ. During normal operation, the word decoder
driver 2 selects one of the word lines WL0-WLn based on the address
signal Add and the first clock signal CLK1. During the burn-in
test, the word decoder driver 2 simultaneously selects all of the
word lines WL0-WLn based on the burn-in control signal BIZ.
[0055] The dummy word control circuit 9 receives the second clock
signal CLK2, the burn-in control signal BIZ, and a selection signal
SEL. Based on the received signals, the dummy word control circuit
9 generates first and second output clock signals CLKD0, CLKD1 and
provides the clock signals CLKD0, CLKD1 to the dummy word decoder
driver 3.
[0056] The sense amplifier control circuit 7, the word control
circuit 8, and the dummy word control circuit 9 constitute a
burn-in test control circuit 110.
[0057] The circuits 7, 8, 9 of the burn-in test control circuit 110
will now be discussed.
[0058] FIG. 4 is a schematic circuit diagram of the word control
circuit 8. The word control circuit 8 includes inverter circuits
10a, 10b, 10c, 10d and NAND circuits 11a, 11b, 11c.
[0059] The inverter circuit 10a, which includes two inverters,
delays the master clock signal CLK received from an external device
and generates the second clock signal CLK2.
[0060] The NAND circuit 11a receives the master clock signal CLK
and the burn-in control signal BIZ which is inverted by the
inverter circuit 10b. The NAND circuit 11a performs a NAND logic
operation and provides the logic operation result to the NAND
circuit 11c. The NAND circuit 11b receives the burn-in control
signal BIZ and the master clock signal CLK via the inverter circuit
10c which includes an even number (e.g., four in the first
embodiment) of inverters. The NAND circuit 11b performs a NAND
logic operation and provides the logic operation result to the NAND
circuit 11c.
[0061] The NAND circuit 11c performs a NAND logic operation based
on the output signals received from the NAND circuits 11a, 11b. The
logic operation result is then provided to the inverter circuit
10d. The inverter circuit 10d, which includes two inverters,
receives the output signal of the NAND circuit 11c and generates
the first clock signal CLK1.
[0062] During normal operation, the word control circuit 8 receives
the burn-in control signal BIZ at a low level. This causes the
output signal of the NAND circuit 11b to go high and the output
signal of the inverter circuit 10b to go high. In this state, the
master clock signal CLK is routed through the inverter circuit 10a
to generate the second clock signal CLK2. Thus, the first clock
signal CLK1 is delayed from the second clock signal CLK2.
[0063] During the burn-in test, the word control circuit 8 receives
the burn-in control signal BIZ at a high level. This causes the
output signal of the NAND circuit 11a to go high. Thus, the master
clock signal CLK is routed through the inverter circuit 10c, the
NAND circuits 11b, 11c, and the inverter circuit 10d to generate
the first clock signal CLK1. Accordingly, the time delay of the
first clock signal CLK1 relative to the second clock signal CLK2
during the burn-in test is longer than that during normal
operation.
[0064] FIG. 5 is a schematic circuit diagram of the dummy word
control circuit 9. The dummy word control circuit 9 includes
inverter circuits 10e, 10f, 10g and NAND circuits 11e, 11f, 11g,
11h.
[0065] The NAND circuit 11e receives the burn-in control circuit
BIZ and the selection signal SEL, and performs a NAND logic
operation. The NAND circuit 11f receives the burn-in control signal
BIZ and the selection signal SEL which is inverted by the inverter
circuit 10e, and performs a NAND logic operation.
[0066] The NAND circuit 11g receives the output signal of the NAND
circuit 11e and the second clock signal CLK2, and performs a NAND
logic operation. The NAND circuit 11h receives the output signal of
the NAND circuit 11f and the second clock signal CLK2, and performs
a NAND logic operation.
[0067] The inverter circuit 10f receives the output signal of the
NAND circuit 11g and generates the first dummy clock signal CLKD0.
The inverter circuit 10g receives the output signal of the NAND
circuit 11h and generates the second dummy clock signal CLKD1.
[0068] During normal operation, the dummy word control circuit 9
receives a low burn-in control signal BIZ. In this state, the
output signals of the NAND circuits 11e, 11f go high. Thus, the
phases of the first and second dummy clock signals CLKD0, CLKD1 are
equal to the phase of the second clock signal CLK2.
[0069] During the burn-in test, the dummy word control circuit 9
receives a high burn-in control signal BIZ. This shifts the levels
of the signals output from the NAND circuits 11e, 11f and causes
the output signals of the NAND circuits 11e, 11f to have inverted
phases.
[0070] When one of the first and second dummy clock output signals
CLKD0, CLKD1 goes low, the other one of the first and second dummy
clock output signals CLKD0, CLKD1 has the same phase as the second
clock signal CLK2.
[0071] FIG. 6 is a schematic circuit diagram of the dummy word
decoder driver 3. The dummy word decoder driver 3 includes NAND
circuits 11i, 11j and inverter circuits 11h, 10i.
[0072] The NAND circuit 11i receives the first dummy clock signal
CLKD0 and an address determination signal ac and performs a NAND
logic operation. The inverter circuit 10h receives the output
signal of the NAND circuit 11i and generates a first dummy word
line selection signal SDWL0, which selects the dummy word line
DWL0.
[0073] The NAND circuit 11j receives the second dummy clock output
signal CLKD1 and an address determination signal /ac and performs a
NAND logic operation. The inverter circuit 10i receives the output
signal of the NAND circuit 11j and generates a second dummy word
line selection signal SDWL1, which selects the dummy word line
DWL1.
[0074] During normal operation, the address determination signals
ac, /ac have inverted phases. For example, the address
determination signal ac is high when an even word line is selected,
and the address determination signal /ac is high when an odd word
line is selected. During the burn-in test, the address
determination signals ac, /ac are both high.
[0075] During normal operation, based on the address of the
selected word line, the dummy word decoder driver 3 inverts one of
the dummy word line selection signals SDWL0, SDWL1 when the first
and second dummy clock signals CLKD0, CLKD1 are inverted.
[0076] During the burn-in test, the dummy word decoder driver 3
inverts one of the dummy word line selection signals SDWL0, SDWL1
when one of first and second dummy clock signals CLKD0, CLKD1 is
inverted.
[0077] FIG. 7 is a schematic circuit diagram of the sense amplifier
control circuit 7. The sense amplifier control circuit 7 includes a
delay circuit 12, an inverter circuit 10j, a p-channel MOS
transistor Tr1, and n-channel MOS transistors Tr2-Tr4.
[0078] The delay circuit 12 receives the second clock signal CLK2,
delays the clock signal CLK2 by a predetermined time, and generates
a sense amplifier activation signal SAE.
[0079] The p-channel MOS transistors Tr1 and the n-channel MOS
transistors Tr2-Tr4 are connected in series between a high
potential power supply FPS1 and a low potential power supply PPS2.
The sense amplifier activation signal SAE is provided to the gate
of the transistor Tr1 via the inverter 10j and to the gate of the
transistor Tr4. An equalizing signal EQ is provided to the gates of
the transistors Tr2, Tr3.
[0080] The drains of the transistors Tr1, Tr2 output a first sense
amplifier voltage PSA, and the drain of the transistor Tr4 outputs
a second sense amplifier voltage NSA. Further, a precharge voltage
EQPPS is output from a node between the transistors Tr2, Tr3.
During the burn-in test, the power supplies PPS1, PPS2 are each
provided with a power supply voltage that produces a potential
difference between the power supplies PPS1, PPS2, which is greater
than that during normal operation.
[0081] When the sense amplifier activation signal SAE goes high,
the transistors Tr1, Tr4 are activated. In this state, the
equalizing signal EQ remains low. As a result, the value of the
first sense amplifier voltage PSA becomes equal to the voltage
value of the high potential power supply PPS1, and the value of the
second sense amplifier voltage NSA becomes equal to the voltage
value of the low potential power supply PPS2. This activates the
sense amplifier 6 (see FIG. 1).
[0082] When the sense amplifier activation signal SAE goes low, the
transistors Tr1, Tr4 are deactivated. In this state, the equalizing
signal EQ goes high, and the transistors Tr2, Tr3 are activated.
This causes the precharge voltage EQPPS to become equal to a median
level between the voltages of the power supplies PPS1, PPS2.
[0083] The time delay produced by the delay circuit 12 is set such
that during normal operation, the sense amplifier 6 is activated
after a predetermined time has elapsed from the time when a word
line is selected.
[0084] FIG. 8 is a schematic circuit diagram of the word decoder
driver 2. The word decoder driver 2 includes a predecoder 13, a
main decoder 14 having a plurality of NAND circuits, and a driver
15 having a plurality of inverter circuits.
[0085] The predecoder 13 receives the address signal Add and the
burn-in control signal BIZ and generates predecoding signals. Each
NAND circuit in the main decoder 14 receives the predecoding
signals and the first clock signal CLK1, and performs a NAND logic
operation.
[0086] The output signal of each NAND circuit is provided to the
associated inverter circuit in the driver 15. The inverter circuits
invert the output signals of the associated NAND circuits and
generate word line selections signals SWL0-SWLn for selecting the
word lines WL0-WLn.
[0087] During normal operation, when the word decoder driver 2
receives the address signal Add and the first clock signal CLK1
goes high, the word decoder driver 2 causes one of the word line
selection signals SWL0-SWLn to go high based on the address signal
Add.
[0088] During the burn-in test, the word decoder driver 2 causes
all of the predecoding signals to go high when the burn-in control
signal BIZ goes high, and causes all of the word line selection
signals SWL0-SWLn to go high when the first clock signal CLK1 goes
high. As a result, all of the word lines WL0-WLn are selected.
[0089] In the first embodiment, during the burn-in test, the first
clock signal CLK1 is provided to the word decoder driver 2 at a
time later than during normal operation. Thus, one of the dummy
word selection lines DWL0, DWL1 is selected in response to the
second clock signal CLK2, and the sense amplifier 6 is then
activated. Subsequently, all of the word lines WL0-WLn are
simultaneously activated.
[0090] The operation of the semiconductor memory device (DRAM) 100
of the first embodiment will now be discussed. FIG. 9 is a combined
timing and waveform chart illustrating the operation of the
semiconductor memory device 100 during the burn-in test.
[0091] During the burn-in test, the high burn-in control signal BIZ
is provided to the semiconductor memory device 100 from an external
device. In this state, when the selection signal SEL goes low, the
first dummy word line selection signal SDWL0 alternatively goes
high and low based on the second clock signal CLK2. The second
dummy word selection signal SDWL1 remains low.
[0092] The first dummy word line DWL0 is selected when the second
clock signal CLK2 goes high. As a result, the capacitive coupling
between the dummy word line DWL0 and the bit line BLZ slightly
increases the potential at the bit line BLZ and produces a small
potential difference between the bit lines BLZ, BLX.
[0093] After the first dummy word line DWL0 is selected, the sense
amplifier activation signal SAE goes high. This activates the sense
amplifier 6 and increases the potential difference between the pair
of bit lines BLZ, BLX to the potential difference between the power
supplies PPS1, PPS2.
[0094] Then, the word decoder driver 2 selects all of the word
lines WL0, WLn based on the first clock signal CLK1, which is
provided by the word control circuit 8. In this state, a stress
voltage is provided respectively between the bit line BLX and the
word lines WL0-WLn and between the bit lines BLZ, BLX.
[0095] Subsequently, when the second clock signal CLK2 goes low,
the selection of the first dummy word line DWL0 ends and the sense
amplifier 6 is deactivated. The sense amplifier control circuit 7
precharges the bit lines BLZ, BLX to a median level between the
power supplies PPS1, PPS2.
[0096] While the selection signal SEL continues to remain low, the
first dummy word line DWL0 is repetitively selected.
[0097] After the selection signal SEL is maintained at the low
level for a predetermined time period, the selection signal SEL
goes high. In this state, the dummy word line selection signal
SDWL1 alternatively goes high and low based on the second clock
signal CLK2, and the dummy word line selection signal SDWL0 remains
low.
[0098] When the second clock signal CLK2 goes high, the dummy word
line DWL1 is selected, and the capacitive coupling between the
second dummy word line DWL1 and the bit line BLX increases the
potential at the bit line BLX.
[0099] Subsequent to the selection of the second dummy word line
DWL1, the sense amplifier activation signal SAE goes high. This
activates the sense amplifier 6 and increases the potential
difference between the pair of bit lines BLX, BLZ to the potential
difference between the power supplies PPS1, PPS2.
[0100] Then, the word decoder driver 2 selects all of the word
lines WL0-WLn based on the first clock signal CLK1 provided by the
word control circuit 8. In this state, a stress voltage is provided
between the bit line BLZ and the word lines WL0-WLn and between the
bit lines BLZ, BLX.
[0101] When the second clock signal CLK2 goes low, the selection of
the second dummy word line DWL1 ends and the sense amplifier 6 is
deactivated. The sense amplifier control circuit 7 precharges the
bit lines BLZ, BLX to the median level between the power supplies
PPS1, PPS2.
[0102] While the selection signal SEL remains high, the second
dummy word line DWL1 is repetitively selected.
[0103] FIG. 10 is a combined timing and waveform chart illustrating
the operation of the semiconductor memory device 100 during a
normal read operation.
[0104] During the normal read operation, a low burn-in control
signal BIZ is provided to the semiconductor memory device 100 from
an external device. This matches the phases of the first and second
dummy clock signals CLKD0, CLKD1 and selects one of the first and
second dummy word lines DWL0, DWL1 based on the address
determination signals ac, /ac.
[0105] Further, based on the master clock signal CLK and the
address signal Add, one of the word lines WL0-WLn is selected at
substantially the same time as the selection of the dummy word
lines DWL0, DWL1.
[0106] Cell information is read from the selected memory cell MC to
one of the bit lines BLZ, BLX. Further, the capacitive coupling of
the dummy cell increases the potential difference between the bit
lines BLZ, BLX.
[0107] The sense amplifier 6 is then activated based on the sense
amplifier activation signal SAE. This amplifies the cell
information read to the bit lines BLZ, BLX.
[0108] The semiconductor memory device 100 of the first embodiment
has the advantages described below.
[0109] (1) The semiconductor memory device 100 generates a stress
voltage based on the burn-in control signal BIZ and the master
clock signal CLK. The stress voltage is provided to the sense
amplifier 6 to perform the burn-in test.
[0110] (2) During the burn-in test, the selection signal SEL
switches between the dummy word lines DWL0, DWL1 to select one of
the bit lines BLZ, BLX that has a high potential. Thus, the
selection of the high potential bit line is facilitated.
[0111] (3) A switch circuit for providing a stress voltage to the
vicinity of the bit lines BLZ, BLX and a signal line for
controlling the switch circuit is not necessary. Thus, the circuit
area of the memory cell array is decreased.
[0112] (4) The sense amplifier 6, which is located between the bit
lines BLZ, BLX, provides a stress voltage to the bit lines BLZ,
BLX. This provides a stable stress voltage to the bit lines BLZ,
BLX and increases the reliability of the burn-in test.
[0113] (5) The number of column decoder input gates does not have
to be increased in order to provide a stress voltage to the bit
lines. Thus, the circuit area of the column decoder does not have
to be increased.
[0114] [Second Embodiment]
[0115] FIG. 11 is a schematic circuit diagram of a semiconductor
memory device 200 according to a second embodiment of the present
invention. The second burn-in test control circuit of the second
embodiment includes a column decoder 16 and a local equalizer
18.
[0116] The memory cell array 1 of the semiconductor memory device
200 has a configuration that is equivalent to that of the memory
cell array 1 of the semiconductor memory device 100 of the first
embodiment. The dummy word lines do not affect the second
embodiment. Thus, the memory cell array 1 and the dummy word lines
will not be described below. Further, the peripheral circuits,
including the word decoder driver 2, the sense amplifier control
circuit 7, the word control circuit 8 and the dummy word control
circuit 9, are similar to those in the first embodiment. Thus,
these circuits will not be described in detail.
[0117] The sense amplifier control circuit 7 is equivalent to that
in the first embodiment. The second clock signal CLK2, generated by
the word control circuit 8 of FIG. 4, is constantly provided to the
sense amplifier control circuit 7.
[0118] Pairs of bit lines BLZ, BLX (only one pair is shown in FIG.
11) are connected to a switch circuit 17. The switch circuit 17 is
opened and closed by an output signal CL of the column decoder 16.
Local data buses LDBZ, LDBX (only one pair is shown in FIG. 11) are
respectively connected to the bit lines BLZ, BLX via the switch
circuit 17.
[0119] The column decoder 16 is configured by eliminating the
driver 15 from the word decoder driver 2 of FIG. 8. The column
decoder 16 receives the address signal Add and the burn-in control
signal BIZ.
[0120] During normal operation, the column decoder 16 connects one
pair of the bit lines BLZ, BLX to the associated pair of the local
data buses LDBZ, LDBX based on the address signal Add. During the
burn-in test, the column decoder 16 receives a high burn-in control
signal BIZ and simultaneously connects every pair of the bit lines
BLZ, BLX to the associated local data buses LDBZ, LDBX.
[0121] The local data buses LDBZ, LDBX are connected to a power
supply PPS3 via high resistance resistors. The local data buses
LDBZ, LDBX are also connected to a power supply PPS4 via a switch
circuit 19, which is opened and closed by output signals LEQZ, LEQX
of the local equalizer 18.
[0122] The potential at the power supply PPS4 is higher than that
at the power supply PPS3. Further, the power supply PPS4 precharges
the local data buses LDBZ, LDBX before the normal read
operation.
[0123] The local equalizer 18 receives a local equalizing signal
LDBEQ, a burn-in control signal BIZ, and a selection signal SEL.
The local equalizer 18 has a circuit configuration equivalent to
that of the dummy word control circuit 9 of FIG. 5. The local
equalizing signal LDBEQ is provided in lieu of the second clock
signal CLK2 to the local equalizer 18.
[0124] During normal operation, the local equalizer 18 receives the
burn-in control signal BIZ at a low level and the local equalizing
signal LDBEQ at a high level. This causes both output signals LEQZ,
LEQX of the local equalizer 18 to go high. As a result, the two
transistors in the switch circuit 19 are activated, and the local
data buses LDBZ, LDBX are precharged to the level of the power
supply PPS4.
[0125] During the burn-in test, when the burn-in control signal BIZ
received by the local equalizer 18 goes high, one of the output
signals LEQZ, LEQX goes high and the other goes low. In other
words, only one of the two transistors of the switch circuit 19 is
activated. The transistor that is to be activated in the switch
circuit 19 is determined by the selection signal SEL.
[0126] When one of the transistors in the switch circuit 19 is
activated, a small potential difference that is substantially equal
to the potential difference between the power supplies PPS4, PPS3
is produced between the local data bus pairs LDBZ, LDBX.
[0127] The local data buses LDBZ, LDBX are respectively connected
to global data buses GDBZ, GDBX via a switch circuit 21. The switch
circuit 21 is opened and closed by an output signal LSW of a local
decoder 20.
[0128] The local decoder 20 receives the address signal Add and the
burn-in control signal BIZ. During normal operation, based on the
address signal Add, one pair of the local data buses LDBZ, LDBX is
connected to the global data buses GDBZ, GDBX.
[0129] Further, during the burn-in test, when the local decoder 20
receives a high burn-in control signal BIZ, the local decoder 20
activates the switch circuit 21 and connects all of the local data
bus lines LDBZ, LDBX to the global data buses GDBZ, GDBX.
[0130] The global data buses GDBZ, GDBX are connected to a power
supply PPS6 via a switch circuit 23 and to a power supply PPS5 via
high resistance resistors. The switch circuit 23 is opened and
closed based on the output signals GEQZ, GEQX of a global equalizer
22.
[0131] The global equalizer 22 receives an equalizing signal GDBEQ
and the burn-in control signal BIZ. The circuit configuration of
the global equalizer 22 is equivalent to that of the dummy word
control circuit 9 of FIG. 5. The global equalizing signal GDBEQ is
provided in lieu of the second clock signal CLK2 to the global
equalizer 22. Further, the selection signal SEL provided to the
input terminals of the NAND circuits 11e, 11f (in FIG. 5) remains
high.
[0132] During normal operation, for example, when the global
equalizing signal GDBEQ goes high, both of the output signals GEQZ,
GEQX of the global equalizer 22 goes high. This activates the
switch circuit 23. Thus, the global data buses GDBZ, GDBX are
precharged to the level of the power supply PPS6.
[0133] During the burn-in test, when the burn-in control signal BIZ
goes high, both of the output signals GEQZ, GEQX go low. This
deactivates the switch circuit 23. Thus, the global data buses
GDBZ, GDBX are disconnected from the power supply PPS6.
[0134] A read amplifier 24a and a write amplifier 24b are connected
to the global data buses GDBZ, GDBX.
[0135] The operation of the semiconductor memory device (DRAM) 200
of the second embodiment will now be discussed.
[0136] During the burn-in test, a small potential difference, which
is substantially equal to the potential difference between the
power supplies PPS4, PPS3, is produced between the local data bus
pairs LDBZ, LDBX by the local equalizer 18 based on a high burn-in
control signal BIZ.
[0137] In this state, the global equalizer 22 deactivates the
switch circuit 23. This prevents interference between the global
data buses GDBZ, GDBX and the local data buses LDBZ, LDBX.
[0138] Further, the column decoder 16 selects and connects to the
local data bus lines LDBZ, LDBX all of the bit lines BLZ, BLX. This
causes the small potential difference between the associated local
data buses LDBZ, LDBX to be applied between the bit lines BLZ,
BLX.
[0139] Then, the sense amplifier 6 is activated and all of the word
lines WL0-WLn are simultaneously selected to perform the burn-in
test. Further, one of the bit lines BLZ, BLX that is to have a high
potential is selected based on the selection signal SEL.
[0140] During the normal read operation, a certain word line and
column are selected based on the address signal Add to read data to
the associated bit lines BLZ, BLX from the corresponding memory
cells MC. The sense amplifier 6 then amplifies the cell information
and provides the amplified cell information to the read amplifier
24a via the local data buses LDBZ, LDBX and the global data buses
GDBZ, GDBX. The read data amplified by the read amplifier 24a is
output to an external device.
[0141] During the normal write operation, the write data received
by the write amplifier 24b from an external device is provided to
the bit lines BLZ, BLX of the column selected by the address signal
Add via the global data buses GDBZ, GDBX and the local data buses
LDBZ, LDBX. The write data received by the bit lines BLZ, BLX is
amplified by the sense amplifier 6 and written to the memory cell
MC of the selected word line.
[0142] The semiconductor memory device 200 has the advantages
described below.
[0143] (1) The semiconductor memory device 200 generates a stress
voltage based on the burn-in control signal BIZ and the master
clock signal CLK. The stress voltage is provided to the sense
amplifier 6 to perform the burn-in test.
[0144] (2) During the burn-in test, the selection signal SEL is
switched from a high level to a low level. This selects one of the
bit lines BLZ, BLX that is to have the high potential.
[0145] (3) A switch circuit for providing a stress voltage to the
vicinity of the bit lines BLZ, BLX and a signal line for
controlling the switch circuit is not necessary. Thus, the circuit
area of the memory cell array is decreased.
[0146] (4) The sense amplifier 6, which is located between the pair
of bit lines BLZ, BLX, provides a stress voltage to the bit lines
BLZ, BLX. This provides a stable stress voltage to the bit lines
BLZ, BLX and increases the reliability of the burn-in test.
[0147] [Third Embodiment]
[0148] FIG. 12 is a schematic block circuit diagram of a
semiconductor memory device 300 according to a third embodiment of
the present invention.
[0149] The semiconductor memory device 300 of the third embodiment
uses a global equalizer 27 in lieu of the local equalizer 25 to
produce a predetermined potential difference between the local data
bus lines LDBZ, LDBX during the burn-in test. The burn-in test
control circuit of the third embodiment includes a column decoder
16 and the global equalizer 27.
[0150] The configuration of the column decoder 16 is similar to
that in the second embodiment. The configuration of the local
equalizer 25 is similar to that of the global equalizer 22 in the
second embodiment, and the local equalizer 25 is provided with the
equalizing signal LDBEQ and the burn-in control signal BIZ.
[0151] During normal operation, the local equalizer 25 precharges
the local data buses LDBZ, LDBX based on the equalizing signal
LDBEQ. During the burn-in test, the local equalizer 25 deactivates
the switch circuit 19 when the burn-in control signal BIZ goes high
and disconnects the local data buses LDBZ, LDBX from the power
supply PPS4.
[0152] During normal operation, a local decoder 26 connects one
pair of the local data buses LDBZ, LDBX to the global data buses
GDBZ, GDBX based on the address signal Add. During the burn-in
test, the local decoder 26 receives a high burn-in control signal
BIZ and connects all of the local data buses LDBZ, LDBX to the
global data buses GDBZ, GDBX.
[0153] The configuration of the global equalizer 27 is similar to
the local equalizer 18 in the second embodiment. During normal
operation, the global equalizer 27 precharges the local data buses
GDBZ, GDBX to the level of the power supply PPS6 based on the
global equalizing signal GDBEQ. During the burn-in test, based on
the burn-in control signal BIZ and the selection signal SEL, the
global equalizer 27 changes the voltage of one of the global data
buses GDBZ, GDBX to the level of the power supply PPS6 and changes
the voltage of the other one of the global data buses GDBZ, GDBX to
the level of the power supply PPS5.
[0154] Accordingly, in the semiconductor memory device 300, during
the burn-in test, the global equalizer 27 produces a small
potential difference between the global data buses GDBZ, GDBX that
is substantially equal to the potential difference between the
power supplies PPS6, PPS5.
[0155] Further, the local decoder 26 connects all of the local data
buses LDBZ, LDBX to the global data buses GDBZ, GDBX. The column
decoder 16 connects all of the bit lines BLZ, BLX to the local data
buses LDBZ, LDBX.
[0156] Therefore, the small potential difference between the global
data buses GDBZ, GDBX becomes substantially equal to the potential
difference between the bit lines BLZ, BLX. When the sense amplifier
6 is activated, all of the word lines WL0-WLn are simultaneously
selected to perform the burn-in test. Further, the selection signal
SEL provided to the global equalizer 27 determines which one of the
bit lines BLZ, BLX is to have the high potential.
[0157] The normal write and read operations are performed in the
same manner as in the second embodiment.
[0158] The semiconductor memory device 300 of the third embodiment
further has the following advantages.
[0159] (1) The number of global equalizers 27, which has input
gates to receive the burn-in control signal BIZ and the selection
signal SEL, is less than that of the local equalizer 25.
Accordingly, the circuit area of peripheral circuits in the third
embodiment is smaller than the circuit area of peripheral circuits
in the second embodiment.
[0160] [Fourth Embodiment]
[0161] FIG. 13 is a schematic circuit diagram of a memory cell
array 400 of a semiconductor memory device according to a fourth
embodiment of the present invention. The burn-in test control
circuit of the fourth embodiment includes a first switch control
circuit and a second switch control circuit.
[0162] FIG. 13 illustrates a DRAM having bit line separation
switches 31a, 31b located between the bit lines BLZ, BLX. Such a
DRAM is described, for example, in Japanese Unexamined Patent
Publication No. 11-232871.
[0163] The read operation of the DRAM will now be described. For
example, when the word line WL0 is selected, only the bit line
separation switch 31a is activated, and cell information is
provided from the bit line BLZ to the sense amplifier 6. The sense
amplifier 6 is then activated. Based on the cell information, the
potential difference between output nodes BLZSA, BLXSA is
amplified, and the cell information is respectively provided to the
data buses DBZ, DBX via column gates 32a, 32b.
[0164] Then, the bit line separation switch 31b is activated, and
the levels of the bit lines BLZ, BLX become complementary. After
the sense amplifier 6 is deactivated, an equalizing switch 37 is
activated by an equalizing signal BR, and the bit lines BLZ, BLX
are reset at the same level, which is substantially equal to a
median level between the sense amplifier voltages PSA, NSA.
[0165] During the burn-in test, the semiconductor memory device of
the fourth embodiment controls the timing of control signals .O
slashed.BT1, .O slashed.BT2 to activate the bit line separation
switches 31a, 31b. This provides a stress voltage to the bit lines
BLZ, BLX from the sense amplifier 6.
[0166] FIGS. 14 and 15 respectively illustrate circuit diagrams of
a first switch control circuit 41 and a second switch control
circuit 42 for controlling the bit switches 31a, 31b of the memory
cell array 400.
[0167] With reference to FIG. 14, a reset signal POR is provided to
the first switch control circuit 41. A first input terminal of a
NOR circuit 33a receives the reset signal POR. The output signal of
the NOR circuit 33a is provided to a first input terminal of the
NOR circuit 33b, and the output signal of the NOR circuit 33b is
provided to a second input terminal of the NOR circuit 33a.
[0168] The reset signal POR goes high for a predetermined time when
the semiconductor memory device is activated. The NOR circuits 33a,
33b constitute a latch circuit. When the semiconductor memory
device is activated, the latch circuit resets node N4, which is the
output terminal of the NOR circuit 33a, to a low level; and resets
node N3, which is an output terminal of the NOR circuit 33b, to a
high level.
[0169] The burn-in control signal BIZ is provided to a first input
terminal of the NOR circuit 33c, and the output signal of the NOR
circuit 33c is provided to a first input terminal of a NAND circuit
34a. The output signal of the NAND circuit 34a is provided to a
second input terminal of the NOR circuit 33c.
[0170] Node N1, which is the output terminal of the NAND circuit
34a, is connected to the power supply Vss via an n-channel MOS
transistor Trn. The gate of the transistor Trn receives the reset
signal POR.
[0171] Accordingly, when the semiconductor memory device is
activated, node N1 is reset to the low level. Further, when the
burn-in control signal BIZ goes high, the NOR circuit 33c and the
NAND circuit 34a latch node N1 at a high level.
[0172] A first input terminal of the NAND circuit 34b receives the
master clock signal CLK via a first delay circuit 35a. The output
signal of the first delay circuit 35a is provided to a second input
terminal of the NAND circuit 34a via a second delay circuit
35b.
[0173] The first delay circuit 35a delays the master clock signal
CLK by a predetermined time and outputs a signal having the same
phase as the master clock signal CLK. The second delay circuit 35b
further delays the delayed master clock signal CLK by another
predetermined time and outputs a signal having a phase inverted
from that of the master clock signal CLK.
[0174] The sense amplifier activation signal SAE is provided to a
second input terminal of the NOR circuit 33b via a third delay
circuit 35c. The third delay circuit 35c delays the activation
signal SAE and outputs a signal having the same phase has the
activation signal SAE.
[0175] The NAND circuit 34b receives the signals from nodes N1, N2,
and N3, performs a NAND operation, and generates a third clock
signal CLK3.
[0176] When the semiconductor memory device is activated, the
levels at nodes N1, N2, and N3 are respectively low, indeterminate,
and high. Thus, the third clock signal CLK3 is high.
[0177] FIG. 16 is a combined timing and waveform chart illustrating
the normal read operation of the semiconductor memory device of the
fourth embodiment.
[0178] During normal operations, the NOR circuit 33c of the first
switch control circuit 41 (in FIG. 14) receives a low burn-in
control signal BIZ, and the output signal of the NOR circuit 33c
goes high. In this state, when the master clock signal CLK goes
high, the first delay circuit 35a causes the level at node N2 to go
high after a predetermined time from the time when the master clock
signal CLK goes high.
[0179] Further, after a predetermined time has elapsed from the
time when the level at node N2 goes high, the output signal of the
second delay circuit 35b goes low, and the level at node N1 goes
high.
[0180] With reference to FIG. 16, a predetermined word line WL is
selected after a predetermined time elapses from when the master
clock CLK goes high. Then, the third clock signal CLK3 goes low
after a predetermined time elapses from when the word line WL is
selected.
[0181] Then, when the sense amplifier activation signal SAE goes
high, the output signal of the third delay circuit 35c goes high
after a predetermined time elapses, and the level at node N3 goes
low. This returns the third clock signal CLK3 to the high level. In
other words, the sense amplifier activation signal SAE goes high,
thereby activating the sense amplifier 6. Thus, after the potential
difference between output nodes BLZSA, BLXSA of the sense amplifier
6 is increased, the third clock signal CLK3 returns to the high
level.
[0182] In the second switch control circuit 42 of FIG. 15, the
address determination signal ac goes high or low based on an
address determination signal that selects word lines. In other
words, the address determination signal ac goes low when the memory
cell MC connected to the bit line BLZ is selected and goes high
when the memory cell MC connected to the bit line BLX is
selected.
[0183] The address determination signal ac is provided to a first
input terminal of a NOR circuit 33d via an inverter circuit 36a and
a transfer gate 37a. The address determination signal ac is also
provided to a first input terminal of a NOR circuit 33e via a
transfer gate 37b.
[0184] The p-channel gates of the transfer gates 37a, 37b receive
the burn-in control signal BIZ. The n-channel gates of the transfer
gates 37a, 37b receive the burn-in control signal BIZ via an
inverter circuit 36b.
[0185] Accordingly, the transfer gates 37a, 37b are deactivated
when the burn-in control signal BIZ goes high, and the transfer
gates 37a, 37b are activated when the burn-in control signal BIZ
goes low. The third clock signal CLK3 is received by second input
terminals of the NOR circuits 33d, 33e.
[0186] A switch selection signal BTSW is provided to a first input
terminal of a NAND circuit 34c via a transfer gate 37c. The switch
selection signal BTSW is also provided to a first input terminal of
a NAND circuit 34d via an inverter circuit 36c and a transfer gate
37d.
[0187] The n-channel gates of the transfer gates 37c, 37d receive
the burn-in control signal BIZ. The p-channel gates of the transfer
gates 37c, 37d receive the burn-in control signal BIZ via the
inverter circuit 36b.
[0188] Therefore, when the burn-in control signal BIZ goes high,
the transfer gates 37a, 37b are activated. When the burn-in control
signal BIZ goes low, the transfer gates 37a, 37b are
deactivated.
[0189] Nodes N5, N6, which are the output terminals of the transfer
gates 37a, 37b respectively, are each connected to the power supply
Vss via an n-channel MOS transistor Trn. The gate of the transistor
Trn receives the burn-in control signal BIZ. Accordingly, when the
burn-in control signal BIZ goes high, the levels at the nodes N5,
N6 go low.
[0190] Nodes N7, N8, which are the output terminals of the transfer
gates 37c, 37d respectively, are each connected to the power supply
Vdd via a p-channel MOS transistor Trp. The gate of the transistor
Trp receives the burn-in control signal BIZ. Accordingly, when the
burn-in control signal BIZ goes low, the levels at the nodes N7, N8
go high.
[0191] The output signal of the NOR circuit 33d is provided to a
second input terminal of the NAND circuit 34c. The output signal of
the NOR circuit 33e is provided to a second input terminal of the
NAND circuit 34d. The NAND circuits 34c, 34d output bit line
control signals .O slashed.BT1, .O slashed.BT2, respectively.
[0192] In the second switch control circuit 42, when the burn-in
control signal BIZ is low during normal operation, the transfer
gates 37a, 37b are activated, and the transfer gates 37c, 37d are
deactivated. Further, the transistor Trp is activated, and the
levels at nodes N7, N8 go high.
[0193] When the clock signal CLK3 goes high, the output signals of
the NOR circuits 33d, 33e both go low, and the bit line control
signals .O slashed.BT1, .O slashed.BT2 both go high. When the third
clock signal CLK3 goes low, based on the address determination
signal ac, one of the bit line control signals .O slashed.BT1, .O
slashed.BT2 goes high, while the other one of the bit line control
signals .O slashed.BT1, .O slashed.BT2 goes low.
[0194] When performing the burn-in test, the burn-in control signal
BIZ goes high. This activates the transfer gates 37c, 37d and
deactivates the transfer gates 37a, 37b. Further, the transistor
Trn is activated and the levels at nodes N5, N6 go low.
[0195] When the third clock signal CLK3 goes high, the output
signals of the NOR circuits 33d, 33e both go low and the bit line
control signals .O slashed.BT1, .O slashed.BT2 both go high.
Further, when the third clock signal CLK3 goes low, based on the
switch selection signal BTWS, one of the bit line control signals
.O slashed.BT1, .O slashed.BT2 goes high, while the other one of
the bit line control signals .O slashed.BT1, .O slashed.BT2 goes
low.
[0196] The burn-in operation of the fourth embodiment will now be
described. FIG. 17 is a combined timing and waveform chart
illustrating the operation of the semiconductor memory device
(DRAM) of the fourth embodiment during the burn-in test.
[0197] After the DRAM is activated, when the burn-in control signal
BIZ provided to the DRAM goes high and the burn-in operation
starts, the bit line control signals .O slashed.BT1, .O slashed.BT2
both go high. Thus, the bit line separations switches 31a, 31b are
both activated. Further, the equalizing signal .O slashed.BR
activates the equalizing switch 37, and the bit lines BLZ, BLX are
precharged to the median potential.
[0198] In this state, when the master clock signal CLK goes high,
the third clock signal CLK3 goes low after a predetermined delay
time, which is determined by the delay circuit 35a. If the second
switch control circuit 42 receives a low switch selection signal
BTSW, the bit line control signal .O slashed.BT1 goes high and the
bit line control signal .O slashed.BT2 goes low. As a result, the
bit line separation switch 31a is activated and the bit line
separation switch 31b is deactivated.
[0199] Then, all of the word lines WL are selected and cell
information is read from the memory cells connected to the bit
lines BLZ, BLX. In this state, all of the memory cells MC have not
yet completed the writing operation and the capacitors of the
memory cells MC have not yet fully stored charge. Thus, the
potentials at the bit lines BLZ, BLX both decrease from the median
level. Since the bit line BLZ is connected to the sense amplifier
6, only the potential at the output node BLZSA of the sense
amplifier 6 decreases. This produces a small potential difference
between the output nodes BLZSA, BLXSA of the sense amplifier 6.
[0200] Then, when the sense amplifier activation signal SAE goes
high and a stress voltage (sense amplifier voltages PSA, NSA) is
provided to the sense amplifier 6, the levels at the output node
BLSZA of the sense amplifier 6 and the bit line BLZ decrease to the
level of the sense amplifier voltage NSA, and the level at the
output node BLXSA increases to the level of the sense amplifier
voltage PSA.
[0201] Then, when the third clock signal CLK3 goes high, the bit
line control signal .O slashed.BT2 goes high and activates the bit
line separation switch 31b. This increases the bit line BLX to the
level of the sense amplifier voltage PSA and provides a stress
voltage between the bit lines BLZ, BLX.
[0202] If the master clock signal CLK goes high when the switch
selection switch BTSW provided to the second switch control circuit
42 is high, the switch control signal .O slashed.BT1 goes low and
the switch control signal .O slashed.BT2 goes high when the third
clock signal CLK3 goes low. As a result, a stress voltage having a
polarity that is inverted from that when the switch selection
signal BTSW is low is provided between the bit lines BLZ, BLX.
[0203] FIG. 16 illustrates the normal read operation performed when
the DRAM receives the low burn-in control signal BIZ. FIG. 16
illustrates an example when the cell information of "0" is read
from the memory cell connected to the bit line BLZ.
[0204] After a predetermined time elapses from the time when the
master clock signal CLK goes high, one of the word lines WL is
selected and cell information is read to one of the bit lines BLZ,
BLX. Then, the third clock signal CLK3 goes low in correspondence
with the operations of the first and second delay circuits 35a,
35b.
[0205] Based on the address determination signal ac, one of the bit
line control signals .O slashed.BT1, .O slashed.BT2 (in FIG. 16, .O
slashed.BT2) goes low. Thus, only the bit line from which cell
information is being read is connected to the sense amplifier 6 by
the associated bit line separation switch.
[0206] Then, the sense amplifier activation signal SAE goes high,
the read information is amplified. When the third clock signal CLK3
goes high, the bit line control signals .O slashed.BT1, .O
slashed.BT2 both return to the high level. In this state, the
potential difference between the bit lines BLZ, BLX is increased,
and the read cell information is output to the data buses DBZ,
DBX.
[0207] Then, the sense amplifier 6 is deactivated and the bit lines
BLZ, BLX are reset to the median potential. The normal read
operation is performed by repeating such procedures.
[0208] The fourth embodiment has the advantages described
below.
[0209] (1) The semiconductor memory device generates a stress
voltage based on the burn-in control signal BIZ and the master
clock signal CLK. The stress voltage is provided to the sense
amplifier 6 to perform the burn-in test.
[0210] (2) During the burn-in test, the selection signal BTSW is
switched to the high level or the low level. This selects one of
the bit lines BLZ, BLX that is to have the high potential.
[0211] (3) A switch circuit for providing a stress voltage to the
vicinity of the bit lines BLZ, BLX and a signal line for
controlling the switch circuit is not necessary. Thus, the circuit
area of the memory cell array 400 is decreased.
[0212] (4) A stable stress voltage is provided to the bit lines
BLZ, BLX by the sense amplifier 6. Thus, the reliability of the
burn-in test is increased.
[0213] [Fifth Embodiment]
[0214] FIG. 18 is a schematic circuit diagram of a memory cell
array 500 of a semiconductor memory device according to a fifth
embodiment of the present invention.
[0215] The memory cell array 500 of the fifth embodiment differs
from the memory cell array 400 of the fourth embodiment only in
that the bit line BLX is connected to the output node BLZSA of the
sense amplifier 6 by the bit line separation switch 31b.
[0216] In the same manner as the fourth embodiment, the burn-in
test is performed based on the operations of the first switch
control circuit 41 of FIG. 14 and the second switch control circuit
42 of FIG. 15. However, in the fifth embodiment, the cell
information read from the bit lines BLZ, BLX is provided to the
output node BLZSA of the sense amplifier 6. Thus, prior to the
burn-in test, different cell information is written to the memory
cell MC connected to the bit line BLZ and to the memory cell
connected to the bit line BLX respectively. One of the bit lines
BLZ, BLX that is to have the high potential is selected based on
the switch selection signal BTSW, so to provide a stress voltage
between the bit lines BLZ, BLX.
[0217] It should be apparent to those skilled in the art that the
present invention may be embodied in many other alternative forms
without departing from the principle and the scope of the
invention. Particularly, it should be understood that the present
invention may be embodied in the following forms.
[0218] In the semiconductor memory device 100 of the first
embodiment, during the burn-in test, a word line other than the
dummy word line may be selected to produce a small potential
difference between the bit lines BLZ, BLX based on the cell
information of the memory cell connected to the selected word
line.
[0219] In the semiconductor memory device of the fourth and fifth
embodiment, after all of the word lines become non-selected, the
sense amplifier activation signal SAE may go high and a stress
voltage may be provided to the sense amplifier 6.
[0220] The present examples and embodiments are to be considered as
illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the
scope and equivalence of the appended claims.
* * * * *