U.S. patent application number 11/307472 was filed with the patent office on 2007-08-09 for p-channel non-volatile memory and operating method thereof.
Invention is credited to Yen-Tai Lin.
Application Number | 20070181937 11/307472 |
Document ID | / |
Family ID | 38333172 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070181937 |
Kind Code |
A1 |
Lin; Yen-Tai |
August 9, 2007 |
P-CHANNEL NON-VOLATILE MEMORY AND OPERATING METHOD THEREOF
Abstract
A P-channel non-volatile memory is described. The P-channel
non-volatile memory includes a substrate, a first memory cell, and
second memory cell. An N-well is disposed over the substrate, and
the first cell and the second cell are disposed over the N-well.
The first memory cell includes a first gate, a first charge storage
structure, a first doped region and a second doped region. The
first doped region and the second doped region are disposed in the
substrate on the respective sides of the first gate. The second
cell includes a second gate, a second charge storage structure, a
third doped region, and the second doped region. The third doped
region and the second doped region are disposed in the substrate on
the respective sides of the second gate. The second cell and the
first cell share the second doped region.
Inventors: |
Lin; Yen-Tai; (Hsinchu,
TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Family ID: |
38333172 |
Appl. No.: |
11/307472 |
Filed: |
February 9, 2006 |
Current U.S.
Class: |
257/321 ;
257/E27.103 |
Current CPC
Class: |
H01L 27/115
20130101 |
Class at
Publication: |
257/321 |
International
Class: |
H01L 29/788 20060101
H01L029/788 |
Claims
1. A P-channel non-volatile memory, comprising: a substrate, having
an N-well therein; a first memory cell, disposed over the N-well,
wherein the first memory cell comprises: a first gate, disposed
over the substrate; a first charge storage structure, disposed
between the first gate and the substrate; and a first doped region
and a second doped region, disposed in the substrate on respective
sides of the first gate; and a second memory cell, disposed over
the N-well, wherein the second memory cell comprises: a second
gate, disposed over the substrate; a second charge storage
structure, disposed between the second gate and the substrate; and
a third doped region and the second doped region, disposed in the
substrate on respective sides of the second gate, wherein the
second memory cell and the first memory cell share the second doped
region.
2. The P-channel non-volatile memory of claim 1, wherein the first
charge storage structure and the second charge storage structure
comprise silicon nitride.
3. The P-channel non-volatile memory of claim 1, wherein the memory
further comprises: a first tunneling dielectric layer, disposed
between the first charge storage structure and the substrate; and a
second tunneling dielectric layer, disposed between the second
charge storage structure and the substrate.
4. The P-channel non-volatile memory of claim 3, wherein the first
tunneling dielectric layer and the second tunneling dielectric
layer comprise silicon oxide.
5. The P-channel non-volatile memory of claim 3, wherein the memory
further comprises a first barrier dielectric layer disposed between
the first gate and the first charge storage structure.
6. The P-channel non-volatile memory of claim 3, wherein the memory
further comprises a second barrier dielectric layer disposed
between the second gate and the second charge storage
structure.
7. The P-channel non-volatile memory of claim 1, wherein the first
doped region is coupled to a bit line and the third doped region is
coupled to another bit line.
8. The P-channel non-volatile memory of claim 1, wherein the first
gate is coupled to a word line and the second gate is coupled to
another word line.
9. A method of operating a P-channel non-volatile memory, the
P-channel non-volatile memory comprising a substrate, an N-well
disposed in the substrate and a serially connected first memory
cell and second memory cell disposed over the N-well, such that a
second doped region is share by the first memory cell and the
second memory cell, and each memory cell comprising a gate disposed
over the substrate, a charge storage structure disposed between the
substrate and the gate, and a first doped region and a third doped
region disposed in the substrate on respective sides of the gate;
the operating method comprising: performing a programming operation
to the first memory cell of the P-channel non-volatile memory by
applying a first voltage to the first doped region of the first
memory cell, applying a second voltage to the gate of the first
memory cell, applying a third voltage to the gate of the second
memory cell, opening up the channel underneath the second memory
cell, applying a fourth voltage to the third doped region of the
second memory cell, and applying a fifth voltage to the N-well,
wherein the fourth voltage is higher than the first voltage, and
the fourth voltage is higher than the second voltage so that a
channel hot hole induced hot electron injection effect is triggered
to program the first memory cell.
10. The operating method of claim 9, wherein the method further
comprises: performing a programming operation to the second memory
cell of the P-channel non-volatile memory by applying the fourth
voltage to the first doped region of the first memory cell,
applying the third voltage to the gate of the first memory cell,
opening up the channel underneath the first memory cell, applying
the second voltage to the gate of the second memory cell, applying
the first voltage to the third doped region of the second memory
cell, and applying the fifth voltage to the N-well so that the
channel hot hole induced hot electron injection mechanism is
triggered to program the second memory cell.
11. The operating method of claim 9, wherein the method further
comprises: performing a erasing operation to the P-channel
non-volatile memory by applying a sixth voltage to the gate of the
first memory cell and applying a seventh voltage to the N-well,
wherein the seventh voltage is sufficiently higher than the sixth
voltage to trigger F-N tunneling to erase the first memory
cell.
12. The operating method of claim 11, wherein the method further
comprises: performing a erasing operation to the P-channel
non-volatile memory by applying an eighth voltage to the gate of
the second memory cell and applying the seventh voltage to the
N-well, wherein the seventh voltage is sufficiently higher than the
eighth voltage to trigger F-N tunneling to erase the second memory
cell.
13. The operating method of claim 12, wherein the method further
comprises: applying a ninth voltage to the first doped region of
the first memory cell or floating the first doped region of the
first memory cell, and applying a tenth voltage to the third doped
region of the second memory cell or floating the third doped region
of the second memory cell.
14. The operating method of claim 9, wherein the method further
comprises: performing a reading operation to the first memory cell
of the P-channel non-volatile memory by applying an eleventh
voltage to the first doped region of the first memory cell,
applying a twelfth voltage to the gate of the first memory cell,
applying a thirteenth voltage to the gate of the second memory
cell, applying a fourteenth voltage to the third doped region of
the second memory cell, and applying a fifteenth voltage to the
N-well, wherein the fourteenth voltage is higher than the eleventh
voltage.
15. The operating method of claim 14, wherein the method further
comprises: performing a reading operation to the second memory cell
of the P-channel non-volatile memory by applying the fourteenth
voltage to the first doped region of the first memory cell,
applying the thirteenth voltage to the gate of the first memory
cell, applying the twelfth voltage to the gate of the second memory
cell, applying the eleventh voltage to the third doped region of
the second memory cell, and applying the fifteenth voltage to the
N-well.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a memory and operating
method thereof. More particularly, the present invention relates to
a P-channel non-volatile memory and operating method thereof.
[0003] 2. Description of the Related Art
[0004] Electrically erasable programmable read-only-memory (EEPROM)
is a type of non-volatile memory that allows multiple data entry,
reading and erasing operations. The stored data will be retained
even after power to the device is removed. Moreover, the access
speed is fast, the storage capacity per unit weight is large and
the access device occupies only a small volume. With these
advantages, EEPROM has become one of the most widely adopted
non-volatile memories for personal computer and electronic
equipment.
[0005] A typical EEPROM has a floating gate and a control gate
fabricated using doped polysilicon. To prevent a conventional
EEPROM from over-erasing in an erasing operation and leading to the
registering of erroneous data, an additional select gate fabricated
using doped polysilicon is disposed on the sidewall of the control
gate and the floating gate above the substrate. In other words, a
select transistor is set up on one side beside the sidewalls of the
control gate and the floating gate.
[0006] In the conventional technique, a charge trapping layer is
sometimes used to replace the polysilicon floating gate. The charge
trapping layer is fabricated using silicon nitride, for example. In
general, the silicon nitride layer is sandwiched between an upper
and a lower silicon oxide layer to form an oxide-nitride-oxide
(ONO) composite layer. This type of device is often referred to as
a silicon/silicon oxide/silicon nitride/silicon oxide/silicon
(SONOS) device.
[0007] However, most SONOS memory devices are N-channel
non-volatile memories. The N-channel non-volatile memory has small
channel current and poor energy utilization. There is only 1
electron injection for the passage of a total of between
10.sup.8.about.10.sup.10 electrons. Therefore, in a low energy
consumption portable electronic product area, the applications of
an N-channel non-volatile memory is rather restricted. If the
memory cell further incorporates a select transistor, the dimension
of the device will increase and accordingly limit the development
of a higher level of integration for the devices.
SUMMARY OF THE INVENTION
[0008] Accordingly, at least one objective of the present invention
is to provide a P-channel non-volatile memory and operating method
thereof, wherein the P-channel non-volatile memory consumes lower
power, has higher operating speed and higher storage capacity.
[0009] At least another objective of the present invention is to
provide a P-channel non-volatile memory, wherein an additional
select transistor is not required for preventing over-erasing
problem.
[0010] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a P-channel non-volatile memory. The
P-channel non-volatile memory includes a substrate, a first memory
cell and a second memory cell. An N-well is disposed over the
substrate, and the first cell and the second cell are disposed over
the N-well. The first memory cell includes a first gate, a first
charge storage structure, a first doped region and a second doped
region. The first gate is disposed over the substrate. The first
charge storage structure is disposed between the first gate and the
substrate. The first doped region and the second doped region are
disposed in the substrate on the respective sides of the first
gate. The second cell includes a second gate, a second charge
storage structure, a third doped region, and the second doped
region. The second gate is disposed over the substrate. The second
charge storage structure is disposed between the second gate and
the substrate. The third doped region and the second doped region
are disposed in the substrate on the respective sides of the second
gate. The second cell and the first cell share the second doped
region.
[0011] According to an embodiment of the present invention, the
first charge storage structure and the second charge storage
structure include silicon nitride, for example.
[0012] According to an embodiment of the present invention, the
P-channel non-volatile memory further includes a first tunneling
dielectric layer disposed between the first charge storage
structure and the substrate and a second tunneling dielectric layer
disposed between the second charge storage structure and the
substrate.
[0013] According to an embodiment of the present invention, the
first tunneling dielectric layer and the second tunneling
dielectric layer include silicon oxide, for example.
[0014] According to an embodiment of the present invention, the
memory further includes a first barrier dielectric layer disposed
between the first gate and the first charge storage structure.
[0015] According to an embodiment of the present invention, the
memory further includes a second barrier dielectric layer disposed
between the second gate and the second charge storage
structure.
[0016] According to an embodiment of the present invention, the
first doped region is coupled to a bit line and the third doped
region is coupled to another bit line.
[0017] According to an embodiment of the present invention, the
first gate is coupled to a word line and the second gate is coupled
to another word line.
[0018] The foregoing P-channel non-volatile memory has a low
operating voltage, a low power rating, and a fast operating speed.
In addition, there is no need for installing a MOS transistor,
which has no storage capacity, to serve as a select transistor.
Thus, the dimension of each memory cell can be substantially
reduced and the level of device integration can be significantly
increased.
[0019] The present invention also provides a method of operating a
P-channel non-volatile memory. The P-channel non-volatile memory
includes a substrate, an N-well disposed in the substrate and a
pair of serially connected first memory cell and a second memory
cell above the N-well. The second doped region is shared by the
first memory cell and the second memory cell. Each memory cell
includes a gate disposed over the substrate, a charge storage
structure disposed between the substrate and the gate and a first
doped region and a third doped region disposed on the respective
side of the gate in the substrate. The operation method includes
the following steps.
[0020] For programming the first memory cell of the P-channel
non-volatile memory, a first voltage is applied to the first doped
region of the first memory cell; a second voltage is applied to the
gate of the first memory cell; a third voltage is applied to the
gate of the second memory cell, the channel underneath the second
memory cell is turned on; a fourth voltage is applied to the third
doped region of the second memory cell; and a fifth voltage is
applied to the N-well. The fourth voltage is higher than the first
voltage and the fourth voltage is higher than the second voltage so
that the channel hot holes can induce a hot electron injection
effect to program the first memory cell.
[0021] For programming the second memory cell of the P-channel
non-volatile memory, the fourth voltage is applied to the first
doped region of the first memory cell; the third voltage is applied
to the gate of the first memory cell, the channel underneath the
first memory cell is turned on; the second voltage is applied to
the gate of the second memory cell; the first voltage is applied to
the third doped region of the second memory cell; and the fifth
voltage is applied to the N-well. Hence, channel hot holes can
induce the hot electron injection mechanism to program the second
memory cell.
[0022] For erasing the data from the first memory cell of the
P-channel non-volatile memory, a sixth voltage is applied to the
gate of the first memory cell; and a seventh voltage is applied to
the N-well. The seventh voltage is higher than the sixth voltage so
that the F-N tunneling effect can be triggered to erase the first
memory cell.
[0023] For erasing the data from the second memory cell of the
P-channel non-volatile memory, an eighth voltage is applied to the
gate of the second memory cell; and the seventh voltage is applied
to the N-well. The seventh voltage is higher than the eighth
voltage so that the F-N tunneling effect can be triggered to erase
the second memory cell.
[0024] According to an embodiment of the present invention,
furthermore, a ninth voltage may be applied to the first doped
region of the first memory cell or the first doped region of the
first memory cell is maintained at a floating state; and a tenth
voltage is applied to the third doped region of the second memory
cell or the third doped region of the second memory cell is
maintained at a floating sate.
[0025] For reading data from the first memory cell of the P-channel
non-volatile memory, an eleventh voltage is applied to the first
doped region of the first memory cell; a twelfth voltage is applied
to the gate of the first memory cell; a thirteenth voltage is
applied to the gate of the second memory cell; a fourteenth voltage
is applied to the third doped region of the second memory; and a
fifteenth voltage is applied to the N-well. The fourteenth voltage
is higher than the eleventh voltage, for example.
[0026] For reading data from the second memory cell of the
P-channel non-volatile memory, the fourteenth voltage is applied to
the first doped region of the first memory cell; the thirteenth
voltage is applied to the gate of the first memory cell; the
twelfth voltage is applied to the gate of the second memory cell;
the eleventh voltage is applied to the third doped region of the
second memory; and the fifteenth voltage is applied to the
N-well.
[0027] According to an embodiment of the present invention, every
pair of serially connected neighboring memory cells forms a memory
unit. When one of the memory cells is being operated, the other
memory cell serves as a select transistor for controlling the
switching of the underlying channel to prevent the operating memory
cell from having program disturbance problem. Furthermore, the
programming operation is carried out using the channel hot hole
induced hot electron mechanism and the erasing action is carried
out through the F-N tunneling effect. As a result, the operating
efficiency of the P-channel non-volatile memory is enhanced.
[0028] The P-channel non-volatile memory has the advantages of a
lower operating voltage, a low power rating and a fast writing
speed. Furthermore, program disturbance problem can be prevented
without requiring any additional select transistor. In addition,
the single polysilicon structure can combine with the
system-on-chip (SOC) technique in the CMOS fabrication process as
well.
[0029] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0031] FIG. 1 is a schematic cross-sectional view of a P-channel
non-volatile memory according to one embodiment of the present
invention.
[0032] FIG. 2A is a schematic cross-sectional view showing the
programming mode of a P-channel non-volatile memory according to
one embodiment of the present invention.
[0033] FIG. 2B is a schematic cross-sectional view showing the
reading mode of a P-channel non-volatile memory according to one
embodiment of the present invention.
[0034] FIG. 2C is a schematic cross-sectional view showing the
erasing mode of a P-channel non-volatile memory according to one
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0036] FIG. 1 is a schematic cross-sectional view of a P-channel
non-volatile memory according to one embodiment of the present
invention. As shown in FIG. 1, the P-channel non-volatile memory
includes a substrate 100, a well 101, a first memory cell 103 and a
second memory cell 105, for example. The substrate 100 is a P-type
substrate, for example. The well 101 is an N-well disposed in the
substrate, for example. The first memory cell 103 and the second
memory cell 105 are disposed over the well 101 and are serially
connected together, for example.
[0037] The first memory cell 103 includes a tunneling dielectric
layer 110a, a charge storage structure 110b, a barrier dielectric
layer 110c, a gate 120, a doped region 105b and a doped region
150c. The tunneling dielectric layer 110a, the charge storage
structure 110b, the barrier dielectric layer 110c and the gate 120
are disposed, from bottom to top, are stacked in sequence over the
substrate 100. The doped region 150b and the doped region 150c are
disposed in the substrate 100 on the respective side of the gate
120, for example.
[0038] The tunneling dielectric layer 110a and the barrier
dielectric layer 110c are fabricated using silicon oxide, for
example. The charge storage structure 110b includes a material
capable of trapping electric charges including, for example,
silicon nitride, silicon oxynitride, tantalum oxide, strontium
titanate or hafnium oxide. The gate 120 includes a conductive
material including, for example, doped polysilicon, metal or metal
oxide. The doped regions 150b and 150c are P-doped regions
containing P-type dopants such as boron,.
[0039] It should be noted that the foregoing barrier dielectric
layer 110c could be selectively disposed according to the device
design. In one embodiment, only the tunneling dielectric layer 110a
and the charge storage structure 110b are disposed between the gate
120 and the substrate 100.
[0040] The second memory cell 105 includes a tunneling dielectric
layer 130a, a charge storage structure 130b, a barrier dielectric
layer 130c, a gate 140, a doped region 150a and the doped region
150b. The tunneling dielectric layer 130a, the charge storage
structure 130b, the barrier dielectric layer 130c and the gate 140,
from bottom to top, are stacked in sequence over the substrate 100.
The doped region 150a and the doped region 150b are disposed in the
substrate 100 on the respective sides of the gate 140, for example.
The second memory cell 105 and the first memory cell 103 share the
same doped region 150b and are serially connected together.
[0041] The tunneling dielectric layer 130a, the charge storage
structure 130b, the barrier dielectric layer 130c and the gate 140
include the same material as the aforementioned tunneling
dielectric layer 110a, the charge storage structure 110b, the
barrier dielectric layer 110c and the gate 120, for example.
Similarly, the barrier dielectric layer 130c can be selectively
disposed according to the actual requirements.
[0042] Spacers 145 are disposed on the respective sidewalls of the
gates 120 and 140, for example. The spacers are fabricated using
silicon oxide, for example. The substrate 100 underneath the
spacers 145 has a doped region 160 disposed therein for minimizing
the short channel effect.
[0043] In one embodiment, the doped region 150a is coupled to a bit
line and the doped region 150c is coupled to another bit line, for
example. The gate 140 of the second memory cell 105 is coupled to a
word line and the gate 120 of the first memory cell 103 is coupled
to another word line, for example. The operation of the P-channel
non-volatile memory includes treating the serially connected first
memory cell 103 and second memory cell 105 as a single memory unit.
In the process of writing data into the first memory cell 103, the
second memory cell 105 serves as a select transistor. When writing
data into the second memory cell 105, the first memory cell 103
serves as a select transistor. In this way, problems such as
erroneous judgment of data or program disturbance can be avoided
during writing, reading or erasing operation.
[0044] It should be noted that the P-channel non-volatile memory in
the present embodiment has a P-type substrate 100 and an N-type
well 101. Obviously, the memory in the present invention is a
P-channel non-volatile memory without an N-type well but have an
N-type substrate.
[0045] The advantages of the aforementioned P-channel non-volatile
memory are a low operating voltage, a low power rating and a fast
operating speed. In addition, the serially connected first memory
cell 103 and second memory cell 105 constitutes a memory unit.
Thus, to program data into or read data from one of the memory
cells, the other memory cell can serve as a select transistor. In
other words, no additional MOS transistor without storage
capability is required to serve as a select transistor. Because of
this arrangement, the dimension of each memory cell can be
significantly reduced leading to a higher level of device
integration.
[0046] Furthermore, the P-channel non-volatile memory of the
present invention has a single-layered polysilicon structure.
Therefore, the memory in the system-on-chip (SOC) can be easily
integrated with the CMOS logic fabrication process.
[0047] In the following, the method of operating the N-channel
non-volatile memory is described. FIG. 2A is a schematic
cross-sectional view showing the programming mode of a P-channel
non-volatile memory according to one embodiment of the present
invention. FIG. 2B is a schematic cross-sectional view showing the
reading mode of a P-channel non-volatile memory according to one
embodiment of the present invention. FIG. 2C is a schematic
cross-sectional view showing the erasing mode of a P-channel
non-volatile memory according to one embodiment of the present
invention.
[0048] In the present invention, the operation of the P-channel
non-volatile memory is illustrated using two serially connected
memory cells 103 and 105 as an example. While writing data into the
second memory cell 105, the first memory cell 103 serves as a
select transistor. On the other hand, while writing data into the
first memory cell 103, the second memory cell 105 serves as a
select transistor. In this way, problems such as erroneous judgment
of data or program disturbance can be avoided during the operation
of the P-channel non-volatile memory.
[0049] As shown in FIG. 2A, for programming data into the second
memory cell 105 of the memory unit, a voltage V.sub.sp of about 0V
is applied to the first doped region of the second memory cell 105,
a voltage V.sub.gp of about 5V is applied to the gate of the second
memory cell 105, a voltage V.sub.g'p of about 0V is applied to the
gate of the first memory cell 103, a voltage V.sub.dp of about 6V
is applied to the third doped region of the first memory cell 103,
and a voltage V.sub.np of about 6V is applied to the N-well. The
first memory cell 103 serves as a select transistor. The
application of a voltage V.sub.g'p to the gate of the first memory
cell 103 turns on the channel underneath the first memory cell 103.
The voltage V.sub.dp of the first memory cell 103 is higher than
the voltage V.sub.sp of the second memory cell 105 and the voltage
V.sub.dp of the first memory cell 103 is higher than the gate
voltage V.sub.gp of the second memory cell 105. As a result,
channel hot holes can induce the hot electron injection effect to
program data into the second memory cell 105.
[0050] To program the first memory cell 103 of the memory unit, the
voltage V.sub.sp originally applied to the first doped region of
the second memory cell 105 for programming the second memory cell
105 is applied to the third doped region of the first memory cell
103. The voltage V.sub.gp originally applied to the gate of the
second memory cell 105 is applied to the gate of the first memory
cell 103. The voltage V.sub.dp originally applied to the third
doped region of the first memory cell 103 is applied to the first
doped region of the second memory cell 105. The voltage V.sub.g'p
originally applied to the gate of the first memory cell 103 is
applied to the gate of the second memory cell 105. In doing so, the
channel underneath the second memory cell 105 is turned on.
Furthermore, the voltage difference between the first doped region
of the second memory cell 105 and the third doped region of the
first memory cell 103, the gate of the first memory cell 103 is
used to trigger channel hot hole induced hot electron injection
effect. Thus, data is programmed into the first memory cell
103.
[0051] As shown in FIG. 2B, for reading data from the second memory
cell 105, a voltage V.sub.sr of about 1.5V is applied to the first
doped region of the second memory cell 105, a voltage V.sub.gr of
about 3.3V is applied to the gate of the second memory cell 105, a
voltage V.sub.g'r of about 0V is applied to the gate of the first
memory cell 103, a voltage V.sub.dr of about 3.3V is applied to the
third doped region of the first memory cell 103, and a voltage
V.sub.nr of about 3.3V is applied to the N-well. The first memory
cell 103 serves as a select transistor to turn on the channel
underneath the first memory cell 103 when the voltage V.sub.g'r is
applied to the gate of the first memory cell 103. The gate voltage
V.sub.gr of the second memory cell 105, the drain voltage V.sub.dr
of the first memory cell 103 and the voltage V.sub.nr of the N-well
are identical. Furthermore, the drain voltage V.sub.dr of the first
memory cell 103 is higher than the source voltage V.sub.sr of the
second memory cell 105. Therefore, by detecting/measuring the
on-off state/current density of the channel underneath the second
memory cell 105, the data stored inside the second memory cell 105
can be judged (`1` or `0`).
[0052] To read data from the first memory cell 103, the voltage
V.sub.sr originally applied to the first doped region of the second
memory cell 105 for reading data from the second memory cell 105 is
applied to the third doped region of the first memory cell 103. The
voltage V.sub.gr originally applied to the gate of the second
memory cell 105 is applied to the gate of the first memory cell
103. The voltage V.sub.dr originally applied to the third doped
region of the first memory cell 103 is applied to the first doped
region of the second memory cell 105. The voltage V.sub.g'r
originally applied to the gate of the first memory cell 103 is
applied to the gate of the second memory cell 105. Thus, the
channel underneath the second memory cell 105 is turned on.
Therefore, by determining/measuring the on-off state/current
density of the channel underneath the first memory cell 103, the
data stored inside the first memory cell 103 can be judged (`1` or
`0`).
[0053] As shown in FIG. 2C, for erasing data from the memory cells
105, 103 of the memory unit, the first doped region of the second
memory cell 105 is floated or a voltage V.sub.se of about 6V is
applied to the first doped region of the second memory cell 105, a
voltage V.sub.ge of about -6V is applied to the gate of the second
memory cell 105, a voltage V.sub.g'e of about -6V is applied to the
gate of the first memory cell 103; the third doped region of the
first memory cell is floated or a voltage V.sub.de of about 6V is
applied to the third doped region of the first memory cell 103, and
a voltage V.sub.ne of about 6V is applied to the N-well. The
voltage V.sub.ne in the N-well or the voltage of V.sub.se, V.sub.de
is higher than the gate voltage V.sub.ge of the second memory cell
105 and the gate voltage V.sub.g'e of the first memory cell 103.
Using the voltage difference between the N-well or cell's channel
and the gate of memory cells 105, 103, F-N tunneling effect is
established in the tunneling oxide of the memory cells 105 and 103.
Hence, electrons are pulled out from the respective memory cells
105, 103 for erasing the data stored within the memory cells 105
and 103.
[0054] In the present embodiment, a P-channel non-volatile memory
having a P-type substrate and an N-well is used in the description.
However, the present invention can also be applied to a P-channel
non-volatile memory without an N-well but having an N-type
substrate. Obviously, if this type of N-type substrate memory is
used, the voltage originally applied to the N-well will have to be
applied to the N-type substrate.
[0055] In aforementioned method of operating the P-channel
non-volatile memory, every pair of serially connected neighboring
memory cells forms a memory unit. When one of the memory cells is
being operated on, the other memory cell serves as a select
transistor for controlling the switching of the underlying channel
to overcome the program disturbance problem. Furthermore, the
programming operation is carried out using the channel hot hole
induced hot electron mechanism and the erasing action is carried
out through the F-N tunneling effect. As a result, the operating
efficiency of the P-channel non-volatile memory is enhanced.
[0056] In summary, the P-channel non-volatile memory of the present
invention uses two serially connected memory cells as a memory unit
so that one of the memory cells can serve as a select transistor
when the other memory cell is operated. Since there is no need to
fabricate a select transistor, the size of each memory cell can be
reduced and thereby further increase the level of integration.
[0057] The P-channel non-volatile memory has the advantages of a
lower operating voltage, a lower power rating and a fast writing
speed. Therefore, it finds many applications in portable electronic
devices. Furthermore, the programming operation is carried out
using the channel hot hole induced hot electron mechanism and the
erasing action is carried out through the F-N tunneling effect. As
a result, the operating efficiency of the P-channel non-volatile
memory is enhanced.
[0058] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
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