Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Amplitude control
Reexamination Certificate
2002-04-12
2004-01-06
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Signal converting, shaping, or generating
Amplitude control
C327S525000
Reexamination Certificate
active
06674316
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to electronic devices and more particularly to improved trim circuitry and methods for trimming electronic devices.
BACKGROUND OF THE INVENTION
Trim circuits are found in many types of electrical devices where a voltage, current, or other operational parameter of a device needs to be adjusted, either during or following manufacturing. Such trim circuitry typically provides a resistance between two nodes in an integrated circuit device, which may be selectively removed, in whole or in part, from the circuit upon application of voltages or currents to trim pads in the device. Trim circuits often employ zener diodes connected in parallel with the resistor to be removed, where the application of an appropriate trim voltage across the diode terminals short-circuits the resistor, sometimes referred to as “blowing” the diode.
In other trim circuits, open-circuits may be selectively created so as to adjust the device performance. In this instance, fuses are often formed in the trim circuit, which can be selectively open circuited by conducting a fuse trim current through the fuse, sometimes referred to as “blowing” the fuse. Such trim circuits, including fuse types and diode types, find application in a wide variety of electrical devices. For instance, trim circuits are often employed in voltage reference or regulator devices wherein one or more reference voltages generated by the device are adjusted during the manufacturing process, such as prior to packaging individual devices.
Many such trim cells may be cascaded in serial fashion, whereby incremental adjustment (e.g., reduction) in the overall resistance may be achieved by sequentially applying such voltages across the diodes to selectively remove incremental resistances from the overall circuit. Such circuits are sometimes referred to as multi-bit trim circuits. For example, a series of such cells, each having a resistor connected in parallel with a zener diode, may be formed in an electrical device between two nodes of interest. An operational parameter associated with the device is measured, and a decision is made as to whether the device needs to be trimmed. If so, one of the diodes is blown, thereby shorting a corresponding one of the series resistors between the device nodes. The device is re-measured, and if further trimming or adjustment of the operating parameter is needed, the process repeats, with further diodes being blown so as to remove further resistance.
A conventional zener diode type trim cell
2
is illustrated in
FIGS. 1A-1C
, consisting of a resistor
4
and a zener diode
6
connected in parallel between two trim pads A and B.
FIGS. 1A and 1C
illustrate the trim cell
2
prior to the diode
6
being shorted, and
FIG. 1B
schematically illustrates the cell
2
after the diode has been sacrificially destroyed by application of a trim voltage across the pads A and B. The structural view of the trim cell
2
in
FIG. 1C
illustrates the layout of the pads A, B, the diode
6
and the resistor
4
in a portion of a typical electrical device semiconductor substrate
10
, where the resistor
4
includes a resistor tank or portion
12
formed in the substrate
10
. The tank
12
may be formed by selectively doping the tank portion
12
with a dopant which is different from the dopant type in the surrounding portions of the substrate
10
. For instance, the tank
12
may be doped with P+ dopants where the surrounding substrate
10
is N type. Conductive contacts
14
and
16
are formed to electrically connect first and second ends of the tank
12
of the resistor
4
to the pads A and B, respectively.
The zener diode
6
consists of a similar tank region
18
doped with the same type dopant used in the resistor tank
12
, and a second region
20
formed in the tank
18
by doping with a dopant of a different type. For example, the diode tank
18
is commonly doped with P type impurities while the second region
20
is doped with N type impurities. The edges of the second region
20
thus form a PN junction of the diode
6
at the interfaces between the P doped material of the tank
18
and the N type material in the second region
20
. The N type doped material in the second region
20
(e.g., the cathode of the diode
6
) is electrically connected to the pad B via an electrical contact
22
, and the opposite end of the diode tank
18
(e.g., the anode) is connected to the pad A via a contact
24
, wherein the contacts
14
,
16
,
22
,
24
and the pads A, B are commonly formed in a metalization layer during fabrication of an electrical device (not shown) of which the trim cell
2
is a part.
In operation, the resistor
4
provides an electrical resistance between the pads A, B, which may be connected to nodes in a circuit (not shown). If it is determined that the electrical resistance needs to be removed, a voltage is applied (e.g., in either direction) across the pads A, B of sufficient level to cause heating of conductive metal near the second region
20
of the diode
6
. For instance, where a DC voltage is applied with pad A held more negative than pad B, a field is established between the contact
22
at the second diode region
20
and the contact
24
at the opposite end of the diode tank
18
. Conductive material (e.g., metal) from the contact
22
melts and spikes through the PN junction of the diode
6
, and migrates through the tank
18
toward the contact
24
, eventually shorting out the diode
6
. This, in turn, short-circuits the resistor
4
in the resistor tank
12
, whereby the electrical resistance of the resistor
4
is effectively removed from the circuit between the pads A and B, as illustrated schematically in FIG.
1
B.
It is noted in
FIG. 1C
that the conventional trim cell
2
occupies a relatively large amount of area in the substrate
10
. This is due at least in part to the separate tanks
12
,
18
used to form the resistor
4
and the diode
6
, respectively. As device densities continue to increase and device sizes and spacings continue to decrease in the design of modern semiconductor devices, the real estate in the substrate
10
becomes more and more costly. Accordingly, it is desirable to provide improved trim cell designs which take up less space in integrated circuits, while allowing the selective removal of electrical resistance therefrom.
Another shortcoming with conventional trim cell architectures is found where multiple cells
2
are configured in serial fashion to allow so-called multi-bit trimming. It is noted in
FIG. 1A
that the two pads A, B must be electrically accessed (e.g., probed) in order to remove the resistance of the resistor
4
(e.g., by blowing the diode
6
) in the trim cell
2
. Thus, where N such trim cells are configured in series, N+1 pads are needed to allow selective access for trimming the individual cells
2
, each of which occupies a significant amount of surface area. Thus, it is also desirable to provide multi-bit trim cells occupying less overall real estate than the series configuration of multiple conventional trim cells such as that illustrated in
FIGS. 1A-1C
.
SUMMARY OF THE INVENTION
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides single and multiple bit trim cells by which electrical resistance can be selectively removed from an electrical circuit in a controlled fashion without occupying excessive amounts of space in an electrical device. Trimming circuitry is provided comprising a resistor and a diode formed in the resistor body having a conductive portion selectively melted to short the resistor. The res
Romas, Jr. Gregory G.
Wang Jian
Garner Jacqueline J.
Wells Kenneth B.
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