U.S. patent application number 10/697012 was filed with the patent office on 2004-05-13 for semiconductor device and method for making the device having an electrically modulated conduction channel.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Adler, Eric, Dunn, James S., Iadanza, Joseph, Lary, Jenifer E..
Application Number | 20040092109 10/697012 |
Document ID | / |
Family ID | 30116143 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040092109 |
Kind Code |
A1 |
Adler, Eric ; et
al. |
May 13, 2004 |
Semiconductor device and method for making the device having an
electrically modulated conduction channel
Abstract
A semiconductor device having a conduction channel which is
electrically modulated. A trench structure is formed within a
substrate enclosing a diffusion region. The trench structure
isolates the devices formed within the diffusion region from the
remaining portion of the substrate. The trench walls are made thin
enough so that the width of the channel within a diffusion region
may be controlled by applying an electrical potential between a
trench wall and the substrate. Transistors formed within the trench
structure have a conduction channel width controlled by the applied
voltage permitting the gain of the transistor to be matched with
the gain of other transistors on the substrate.
Inventors: |
Adler, Eric; (Jericho,
VT) ; Dunn, James S.; (Jericho, VT) ; Iadanza,
Joseph; (Hinesburg, VT) ; Lary, Jenifer E.;
(Hinesburg, VT) |
Correspondence
Address: |
CONNOLLY BOVE LODGE & HUTZ LLP
SUITE 800
1990 M STREET NW
WASHINGTON
DC
20036-3425
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
30116143 |
Appl. No.: |
10/697012 |
Filed: |
October 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10697012 |
Oct 31, 2003 |
|
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|
09467537 |
Dec 20, 1999 |
|
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6683345 |
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Current U.S.
Class: |
438/689 ;
257/E21.618; 257/E21.628; 257/E27.047; 257/E29.255;
257/E29.326 |
Current CPC
Class: |
H01L 21/823412 20130101;
H03M 1/0604 20130101; H03M 1/66 20130101; H01L 27/0802 20130101;
H01L 21/823481 20130101; H01L 29/8605 20130101; H01L 29/78
20130101 |
Class at
Publication: |
438/689 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed is:
1. A semiconductor device having a conduction channel having a
width which is electrically modulated comprising: a substrate
including a diffusion region; a gate disposed over said diffusion
region; and a trench structure formed in said substrate, enclosing
said diffusion region, said trench structure modulating a width of
a first channel in said diffusion region below said gate, in
response to a voltage potential applied between said trench
structure and said substrate which is capacitively coupled to said
channel.
2. The semiconductor device according to claim 1 wherein said
trench structure comprises a trench etched in said substrate and
filled with polysilicon, having an oxide liner insulating said
trench from said substrate.
3. The semiconductor device according to claim 1 further comprising
a plurality of gates over said diffusion region, forming a
plurality of channels which are commonly controlled with said first
channel by said voltage potential.
4. A semiconductor device for providing first and second matched
sets of resistors comprising: a common substrate including a first
and second trench structures enclosing first and second diffusion
regions; a first plurality of resistors in said first diffusion
region; a second plurality of resistors in said second diffusion
region; and first and second control terminals connected to said
first and second trench structures for applying first and second
control voltages between said trench structures and said substrate,
whereby a channel width of each of said resistors of a plurality of
resistors may be controlled.
5. The semiconductor device according to claim 4 further
comprising: a first differential amplifier having an inverting
input connected to a source of voltage through a first resistor of
said first diffusion region, a non inverting input connected to
ground through a second resistor of said first diffusion region,
and an output terminal connected to said first control terminal;
and a second differential amplifier having a non inverting input
connected to said first differential amplifier inverting input and
to a source of voltage through a first resistor of said second
diffusion region, an inverting input connected to said first
differential amplifier non inverting input and to ground through a
second resistor in said second diffusion region, and an output
terminal serially connected to said second control terminal.
6. A circuit on each of different areas of said substrate having
transistors with matching gains comprising: a first transistor in
each of said different areas, each of said first transistors having
a substantially equal area and substantially the same gain, which
produces substantially the same current in response to the same
voltage conditions supplied to each of said first transistors;
second and third transistors located in a trench in each of said
different areas, having substantially the same gain controlled by a
voltage applied to said trench, said second transistor being
serially connected with said first transistor and having a gate
connected to the gate of said first transistor; and a feedback
voltage connected from said first transistor source to said trench,
providing a voltage which modulates the channel width of said
second and third voltage transistors, and which produces
substantially the same current through said first and second
transistors of said different areas, thereby producing
substantially the same gain for said third transistors of different
areas of said substrate.
7. The circuit according to claim 6 further comprising a current
source serially connected with one of said third transistors and a
gate of said one third transistor, and a connection between gates
of said third transistors which establishes a common current
through all of said third transistors.
8. The circuit according to claim 6 wherein said feedback voltage
is derived from the serial connection of said first and second
transistors.
9. The circuit according to claim 6 wherein said second and third
transistors occupy substantially less area than said first
transistor.
10. The circuit according to claim 6 wherein said first and second
transistor gates are connected to a common source of voltage.
11. A current source for a branch of a digital to analog converter
comprising: a transistor located within a trench structure, said
transistor having a gate connection connected to a source of gate
voltage, and a source and drain connected to supply a current to
first and second transistors, one of which supplies current to an
output terminal, the other of which diverts current from said
output terminal, in response to a respective first and second state
of a digital data bit; and means for supplying a bias voltage to
said trench to modulate the effective width of said transistor in
said trench structure whereby said current diverted to said output
terminal may be set with respect to other branches of said digital
to analog converter.
12. The current source for a branch of a digital to analog
converter according to claim 11 wherein said means for supplying a
bias voltage is a bias circuit which may be trimmed to provide a
bias voltage which will set the current level for said branch.
13. In a digital to analog converter circuit which produces a
voltage proportional to an input digital signal, a voltage to
current converter circuit comprising: at least one transistor in a
trench isolation structure, having drain source connections
connected between a source of voltage and a common output terminal,
and a gate terminal connected to a source of bias voltage; and said
trench structure receiving said digital to analog voltage
proportional to said input digital signal, said voltage modulating
a channel width of said transistor, whereby an output current is
produced by said common output terminal representing said input
digital signal.
14. The voltage to current converter according to claim 13
comprising a second transistor in said trench structure connected
in parallel with said one transistor.
15. An IC chip comprising: a substrate; a plurality of devices
formed in the substrate and each including a channel for conducting
current, the channel having a length and a width; a plurality of
voltage terminals for providing a controllable voltage level; and a
plurality of conductive regions formed in the substrate and each
connected to one of the voltage terminals, wherein the conductive
regions are each formed sufficiently nearby at least one of the
channels such that a voltage level of the conductive region
modulates the width of said at least one of the nearby channels in
response to a voltage level provided to the conductive region by
said one of the voltage terminals.
16. The chip of claim 15, wherein the plurality of devices are FETs
each having diffusion regions formed in the substrate at two ends
of the length of its channel and each having a gate formed above
its channel.
17. The chip of claim 15, wherein the plurality of devices are
resistors each having terminals formed in the substrate at two ends
of the length of its channel.
18. The chip of claim 15, wherein the channel is insulated from its
nearby conductive region by an insulative material.
19. The chip of claim 18, wherein the nearby conductive region
surrounds the channel.
20. A method for making a semiconductor chip comprising: forming a
diffusion region in a semiconductor substrate; forming an insulated
trench structure in said substrate which surrounds said diffusion
region; and forming electrical connections on said trench structure
and said substrate which receive a control voltage whereby an
electric field is produced to control a current flowing in said
diffusion region.
21. The method for making a semiconductor chip according to claim
20, further comprising source and drain regions formed in said
diffusion region on each side of said gate.
22. The method for making a semiconductor chip according to claim
20, wherein said diffusion region forms a resistor which has a
resistance controlled in response to said control voltage.
23. The method for making a semiconductor chip according to claim
20, wherein said diffusion layer is formed in a well of polysilicon
deposited in said trench structure.
24. A method for making a semiconductor chip comprising: forming
first and second diffusion regions in a semiconductor substrate;
forming a trench structure around said first and second diffusion
regions; and forming a contact on said trench structure and said
substrate for controlling current through said diffusion
regions.
25. The method for making a semiconductor chip according to claim
24, further comprising: forming first and second gates over said
first and second diffusion regions.
26. A method for making a semiconductor chip comprising: forming
multiple trench structures on a substrate; forming multiple
diffusion regions in said trench structures in said substrate; and
forming multiple contacts on each of said trench structures and
said substrate for controlling current through said diffusion
regions.
27. The method for making a semiconductor chip according to claim
26, further comprising: forming a gate electrode over each of said
diffusion regions; and forming drain and source connections on
opposite sides of said gate electrodes.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to the MOS semiconductor art.
Specifically, a semiconductor device having an electrically
controllable channel width is described which may be used in
applications where matching the electrical parameters of devices on
a single integrated circuit is desirable.
[0002] Integrated circuits having MOS derived components have
manufacturing tolerances which vary with position on the device,
and transistors located on one portion of a semiconductor substrate
may have different gain characteristics than those in other
locations on the substrate. Variations in the device
characteristics across the integrated circuit result from random
and systematic variations in manufacturing processes. The process
variations include photolithographic image size variations, etch
image size variations, ion implant dopant level variations and the
thickness of deposited or grown films. These variations become
increasingly significant as the area of the devices decreases.
[0003] Some electronic circuit applications require that the
transistors have an essentially matched gain. One such application
is a digital to analog converter, wherein a ladder network is
provided generating a plurality of reference currents from a
constant reference current distributed throughout the integrated
circuit. A designer will provide for a single source of current as
the reference value, and the value of the reference current is
reproduced in locations throughout the integrated circuit.
Variations in transistor gain across the integrated circuit will
result in random and systematic variations in reference currents
which are replicated throughout the device.
[0004] The present invention has been derived to provide
semiconductor devices, such as a transistor or a resistor, having
electrical properties which can be matched to other similar devices
located on the substrate.
SUMMARY OF THE INVENTION
[0005] The present invention provides for a semiconductor device
having an electrically modulated conduction channel. The device is
located within a trench structure formed in a substrate of an MOS
integrated circuit, and a diffusion region within the trench
structure is electrically modulated by applying a voltage between
the trench and substrate.
[0006] In accordance with one embodiment of the invention, the
device located within the trench structure may be an FET
transistor, having a gate deposited over the diffusion region. The
channel width below the gate can therefore be modulated by applying
an electrical potential between the trench structure and the
substrate, producing a change in the transistor gain. Accordingly,
the gain of the device may be effectively set by varying the
voltage potential between the trench structure and the substrate to
match the gain of other transistors on the substrate.
[0007] In accordance with the invention, a pair of transistors
having similar characteristics may be formed within the trench. If
a known gain is established in one of the transistors, by
controlling the trench to substrate potential, so that a known
current flows therethrough, the gain on the other transistor is
commonly controlled by the same potential between the trench and
substrate, and the other transistor can be used to generate a
reference current. Different pairs of transistors located in other
trenches on the substrate may be set to the same gain, if the known
current is set in one of the transistors. The remaining transistor
of each pair of transistors in a trench may be advantageously used
to generate the same reference current if their gate connections
are commonly connected.
[0008] In yet another embodiment of the invention, the trench
structure may include multiple diffusion regions which serve as
resistor controlled from a common control voltage.
[0009] In still another embodiment of the invention, each diffusion
region is surrounded by a single trench structure which controls
the diffusion region.
DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A is a plan view of a channel modulated FET transistor
in accordance with the preferred embodiment;
[0011] FIG. 1B illustrates a section view of the transistor of FIG.
1A;
[0012] FIG. 1C illustrates the effect of applying positive
potential between the trench and substrate;
[0013] FIG. 1D illustrates the effect of applying a negative
potential between the trench and the substrate;
[0014] FIG. 2 illustrates an application for controlling the gain
of one of a pair of transistor devices in accordance with the
preferred embodiment;
[0015] FIG. 3 is a schematic illustration of the circuit of FIG.
2;
[0016] FIG. 4 illustrates another embodiment of the invention for
matching the value of resistors at different locations on the
substrate;
[0017] FIG. 5 is a top view of one of the resistor banks of the
device of FIG. 4;
[0018] FIG. 6A is a section view of the device of FIG. 5 along
lines A-A;
[0019] FIG. 6B is a second section view along lines B-B of the
resistor bank of FIG. 5;
[0020] FIG. 7 represents a prior art digital-to-analog converter
which may be improved utilizing one embodiment of the
invention;
[0021] FIG. 8 illustrates an improved digital-to-analog converter
which converts a voltage output to a current output having a high
linearity; and
[0022] FIG. 9 illustrates an improved digital-to-analog converter
having current sources which are channel modulated to improve the
linearity.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] A transistor having an electrically modulated channel in
accordance with the present invention is shown more particularly in
FIGS. 1A through 1D. Referring now to FIGS. 1A through 1D, a trench
structure 12 is shown formed in an integrated circuit substrate.
The trench has a depth D of approximately 0.3 to 0.4.mu.. A
connection 21 is formed on the trench, to which a voltage may be
applied, and a similar connection 22 is provided on the substrate
25. A diffusion region 11 is formed in the substrate, surrounded by
the trench, and a gate 18 is formed over the diffusion region 11.
Source and drain regions are provided on either side of the gate 18
to form a transistor.
[0024] As illustrated in FIGS. 1B-1D, the trench is filled with a
polysilicon material 26 and includes a thin oxide layer along the
inner and outer side walls. The electric field created between the
trench and substrate modulates the channel width as shown in FIGS.
1C and 1D. In response to the application of a positive potential
between terminals 21 and 22, a thin P=layer forms at the trench
body interface, and the gate will have a greater effective width
than with no potential applied. As shown in FIG. 1D, when a
negative voltage potential is applied between the trench contact 21
and substrate 25, a thin P.sup.+ layer forms at the trench body
interface, effectively narrowing the width of the gate, and the
channel underneath the gate.
[0025] The narrowing width does not effect the threshold for the
transistor, if the transistor width is above a predetermined
factor. Control over channel width, in turn, provides a direct
control over the gain (g.sub.m) of the device.
[0026] An application for the electrically modulated transistor
which provides a controlled reference current at various points
within the integrated circuit is shown in FIGS. 2 and 3. FIG. 2
illustrates a basic building block for providing transistors having
matched gains in different portions of the integrated circuit
substrate. Q2' and Q3', as well as Q1', are located on a different
portion of the integrated circuit substrate than Q1, Q2 and Q3.
However, both circuits are capable of generating the identical
current through Q3 and Q3' by establishing the identical gain for
Q3 and Q3' and a common gate to source voltage, even though the
transistors may not be matched at the time of manufacture.
[0027] The circuit of FIG. 3 takes advantage of the fact that
because Q1 and Q1' occupy a large area of the substrate, their gain
characteristics (g.sub.m) are more closely matched, as the degree
of mismatched generally proportional to: 1 1 A
[0028] where A is the area of the transistor on the substrate. Q1
and Q1' have gates connected to the same reference voltage 42,
which may be Vdd/2, and identical currents are established through
Q1',Q1 and the serial connection of Q2' and Q2. The trench
containing Q2 and Q3 is modulated with the drain voltage of Q1, so
that Q2 assumes a gain value sufficient to support a current
determined by the reference voltage 42 on the gate connection of Q1
and Q1'. While Q2 and Q2' may not be matched, their gains will be
set to be the same in order to derive the same source-drain current
through Q1', Q2', and Q1 and Q2. Process variations between Q2 and
Q3 are minimal, even though the devices have a much smaller area on
the substrate than Q1. Once the gain of Q2 is fixed, the gain of Q3
which because of its proximity to Q2 is substantially the same as
Q2, is also fixed.
[0029] FIG. 2 shows the general configuration where the two
transistors, Q2 and Q3, are included within the diffusion area 11.
Each of the transistors includes a gate 18, 180, as well as a
source drain region 17-19 within the diffusion area 11. The current
source 35 carrying the reference current connects to the drain of
Q3. The source of Q2 and Q3 is connected to the common ground 32.
Each of the nFETs Q2 and Q3 are controlled by a current from Q1,
which is a pFET within an N well 36. The drain of Q1 is connected
to the drain of Q2, through terminal 33, as well as to the trench
12. Current flowing through Q1 is established by the reference
voltage connected to terminal 42, and the gain of Q1 establishes a
voltage on the trench which in turn sets the gain of Q2 sufficient
to carry the current of Q1. As illustrated in FIG. 3, the trench is
effectively a capacitor, coupling the same electrostatic charge
across a conduction channel, thereby setting the same gain for Q2
and Q3.
[0030] The illustrated circuit of FIG. 3, duplicating the device is
Q3', Q2' and Q1', permits the identical current of current source
35 to be established in RL. As Q1' has a large area equal to the
area of Q1, it has substantially the same gain as Q1, and the same
current is established for Q1'. This, in turn, sets the gain of Q2'
to be the same as Q2 by changing the trench voltage to compensate
for process variation. Because of Q2' proximity to Q3', it
establishes the same gain for Q3' which has a gate to source
voltage the same as Q3. Accordingly, RL must carry the same drain
source current as current source 35 provides.
[0031] It is also possible to include more than two transistors in
a trench which will permit other circuits to be implemented which
need transistors having matching gains.
[0032] The foregoing circuit permits the duplication of a reference
current 35 in numerous places in the integrated circuit by
establishing a large area transistor such as Q1 and Q1' in each
location which will have the same gain, and carry the same current,
given the fact that larger area transistors are already matched.
Connecting one of the two transistors within a trench in series
with one of the larger transistors, so that the series connected
transistors carry the same current, will establish the same gain
for the remaining transistor in the trench. The current through
each of the drain source circuit of the remaining transistor in
each trench will be the same when the gates of these transistors
are connected together.
[0033] The foregoing principles may also be applied to control
devices which are not field effect transistors. For instance, FIG.
4 illustrates a circuit which matches the resistance values in one
location of the substrate to resistance values at another location
on the substrate. Due to the aforesaid process variations during
the manufacture of the integrated circuit, the resistor values may
not be well matched. The implementation according to FIG. 4 permits
a trimming of the value by changing an electrical potential
associated with resistors on one portion of the substrate with
respect to an electrical potential of another portion of the
substrate containing another set of resistors.
[0034] Referring now specifically to FIG. 4, a bank of resistors
50-54 are shown which are located on a different portion of the
circuit substrate than resistors 65-69. Each bank of resistors
50-54, 65-69 are located within a trench 56, 71 of a substrate. The
trench walls which enclose each of the resistor banks are connected
via a respective connection 63, 70 to the output of the first and
second differential amplifiers 48, 49. Differential amplifiers 48
and 49 provide a potential for modulating the width of the
resistors of a respective resistor bank. Thus, where the resistors
of those banks are to be matched with respect to each other, i.e.,
resistor 50=69, 56=68, 51=67, . . . a control voltage may be
derived for modulating the width of each of the resistors of a
resistor bank.
[0035] In the circuit of FIG. 4 the resistance of R1 is set equal
to the resistance R2 and R3 is set equal to R4, by virtue of the
fact that differential amplifiers 48 and 49 will assume output
values which produce 0 volts between the inverting and
non-inverting inputs of amplifiers 48 and 49. The potential applied
to the trench walls produces an electrostatic field between the
walls of trenches 56, 69 and the substrate 72, effectively
modifying the width and resistance value of the resistors within a
trench.
[0036] FIGS. 5, 6A and 6B show in greater detail the construction
of a given trench 56 and the individual resistors within the
trench. Referring now to FIGS. 5, 6A and 6B, the resistors comprise
a diffusion layer 59, shown as doped N+, formed within a well of
polysilicon 60 deposited within the trench 56. The diffusion 59 is
connected to contacts 61 and 64, formed through an oxide layer 60.
Contacts 61 and 64 provide for connections to the resistor.
[0037] The trench is filled with polysilicon, and each of the
resistors 50-54 are separated from the trench by a thin oxide layer
shown as 50a for resistor 50. Accordingly, a potential applied
between terminal 63 and the substrate 72 provides an electrostatic
field for modulating the width of each resistor of a bank. Thus,
the two banks of resistors have matched pairs of resistors at
different locations on the substrate. As shown in FIG. 6B, changes
in the trench voltage deplete the N+ region near the trench walls,
increasing the resistance of each resistor.
[0038] The foregoing embodiments utilize isolation trenches which
are in use in semiconductor manufacturing processes. Formation of
shallow isolation trenches throughout the substrate permit the
creation of actively controlled components such as the foregoing.
In those instances where the components are not to be controlled,
the trench walls may be tied to the same potential as the
substrate.
[0039] The process of forming such shallow isolation trenches are
conventional, and well known. Such devices are currently used as
capacitors, and for other applications where isolation of one
component from another is necessary.
[0040] A transistor having an electrically modulated channel is
useful in digital-to-analog converters. A prior art
digital-to-analog converter (DAC) is shown more particularly in
FIG. 7. The device of FIG. 7 includes a digital decoder 74, which
creates pairs of control signals for each digit of an input signal.
The pairs of control signals control current flow in one or the
other transistor of a current branch. Each current branch includes
a current source, operated in saturation at a value which is
weighted according to the order of an applied digit, which supplies
current through first or second transistors and converts the bit
into a current supplied to output 88. The lowest order bit controls
transistors 80, 81 to supply current from current source transistor
75. Higher order bits are represented by the current flow in the
current branch including source 76, transistors 82 and 83, and the
current flow in the branch including current source 77, and
transistors 84 and 85. The current source transistors 75, 76 and
77, are all driven by a common analog bias voltage applied to
common gates 89. Depending upon the digital value and its
complement, current is either directed to the output 88 or to
ground. Shunting current which is not directed to the output 88 to
ground provides a reduction in unwanted transients, when switching
current to the output 88 through one of the transistors 80, 82 or
84.
[0041] The accuracy of the device depends in part on the ability to
generate a known and precise current through each branch from
current sources 75, 76 and 77. Typically, this is realized by
having transistors 75, 76 and 77 quite wide, making their width (w)
proportional to the value of current needed in the respective
branch. The unfortunate consequence is the use of a large amount of
chip area. Additionally, due to process variations, the transistors
75, 76 and 77 produce a variation in currents which reduce the
linearity of the output.
[0042] The transistor having an electrically modulated channel may
be useful in digital-to-analog to converter circuits for reducing
the spread in current source gains, and the resulting decrease in
DAC linearity, linearity being a measure of the output value with
certainty, given a known digital input as determined across the
digital input range.
[0043] One approach of using the device in accordance with the
invention is shown in FIG. 8. A digital signal is decoded in a
digital decoder 74 and used to derive an output voltage. The
devices 90, 91 and 92 comprise a low power voltage DAC. The low
power voltage DAC, known to those skilled in the art, creates an
output voltage which in some applications needs to be converted to
a current. The lower power voltage DAC charges a capacitor bank 91
to a voltage proportional to the input digital signal. A charge
stored on the capacitor bank 91 is integrated in an integrator 92,
and the value is sampled and held in the sample/hold circuit 93
while charge/integration takes place.
[0044] The low power voltage DAC utilizes less chip area than the
device of FIG. 7, even when the voltage to current converter using
a transistor having a modulated channel width is employed. The
voltage output from the low power voltage DAC 90 modulates the
width of transistors 75a and 80a. An output node 88a provides the
current which is proportional to the voltage applied to the trench
connection 94.
[0045] The result is a current output which, with proper centering
of the trench bias, provides a current which oscillates around the
current value set by the DC voltage component on trench contact 94.
The voltage to current converter 90 provides a current midpoint,
reducing thermal and electromigration as well as an improvement in
power consumption over the prior art device in FIG. 7. The
disadvantages of the circuit of FIG. 8, however, include its
inability to produce a 0 current at its output, and a reduced high
frequency capability due to the fact that the system relies upon
the charge and discharge of a capacitor bank 91.
[0046] FIG. 9 represents a more advantageous application of a
trench modulated transistor in accordance with the present
invention in a DAC. As shown in FIG. 9, each of the current sources
includes a transistor 75, 76 and 77, having its own trench bias
voltage. By applying an individual trench bias to each of
transistors 75, 76 and 77, it is possible to compensate for
manufacturing tolerances which produce transistors having a width
deviating from the desired width. Thus, the current through each of
the branches may be advantageously trimmed by controlling the
trench bias produced by bias network 100. The bias voltage may be
controlled using laser trimming, or through a fuse blow or other
known techniques for changing the value of a bias network connected
to a source of bias voltage or using a biasing circuit such as
shown in FIGS. 2 and 3.
[0047] The foregoing description of the invention illustrates and
describes the present invention. Additionally, the disclosure shows
and describes only the preferred embodiments of the invention, but
as aforementioned, it is to be understood that the invention is
capable of use in various other combinations, modifications, and
environments and is capable of changes or modifications within the
scope of the inventive concept as expressed herein, commensurate
with the above teachings, and/or the skill or knowledge of the
relevant art. The embodiments described hereinabove are further
intended to explain best modes known of practicing the invention
and to enable others skilled in the art to utilize the invention in
such, or other, embodiments and with the various modifications
required by the particular applications or uses of the invention.
Accordingly, the description is not intended to limit the invention
to the form disclosed herein. Also, it is intended that the
appended claims be construed to include alternative
embodiments.
* * * * *