Method for trimming resistors

Abstract

There is provided a method and circuit for trimming a functional resistor on a thermally isolated micro-platform such that a second functional resistor on the same micro-platform remains substantially untrimmed; a method and circuit for providing and trimming a circuit such that at least two circuit elements of the circuit are subjected to a same operating environment and the operating environment is compensated for by distributing heat generated during operation of the circuit among the two circuit elements; a method and circuit for trimming a functional resistor on a thermally-isolated micro-platform such that a constant temperature distribution is obtained across the functional resistor; and a method and circuit for calculating a temperature coefficient of resistance of a functional resistor.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a divisional of U.S. patent application Ser. No. 10 / 796,421 filed on Mar. 10, 2004, which is a continuation of PCT application PCT / CA02 / 01366 filed on Sep. 10, 2002 designating the United States of America, which claims priority of U.S. provisional application No. 60 / 317,969, filed on Sep. 10, 2001.FIELD OF THE INVENTION [0002] The invention relates to the trimming of a resistor or resistors, suitable for use at any level of the manufacturer-to-user chain. More specifically, it relates to trimming by resistive heating using electric current in the resistor itself or in an adjacent resistor. BACKGROUND OF THE INVENTION [0003] The trimming (adjustment) of resistors is a widely used procedure in the manufacture of microelectronics and electronic components, and in common design of user circuits, especially where precision calibration is desired. In principle, one trims the resistor until an observable local or gl...

AI Technical Summary

Benefits of technology

[0018] Accordingly, an object of the present invention is to perform effective trimming of functional resistors made from unstable material, wherein the trimming behavior depends sensitively on temperature above a certain threshold, by obtaining a temperature relatively constant with time in the targeted element, and by obtaining a relatively flat spatial temperature profile in the targeted element. This should lead to the effective trimming of resistors in a wider range of devices, and in a wider range of circumstances, and the enabling of practical user-trimming and field-trimming of applications devices such as resistor dividers, trimpots, resistor networks, op-amps, instrumentation op-amps, reference voltage sources, DAC / ADC's, signal conditioning circuits, programmable gain amplifiers, piezoresistors, and sensors.

[0020] It is also an object of the present invention to reduce the amount of power needed to accomplish trimming.

[0031] According to a fifth broad aspect of the present invention, there is provided a circuit for trimming circuit elements, the circuit comprising: at least one thermally-isolated micro-platform on a substrate; at least two resistive elements with non-zero temperature induced drift on said at least one thermally-isolated micro-platform, such that said at least two resistive elements on said at least one micro-platform are subjected to a substantially same operating environment, at least one of said at least two resistive elements on said at least one micro-platform being thermally trimmable; and trimming circuitry for thermally trimming said at least one of said at least two resistive elements; wherein said at least two resistive elements are connected together in said circuit in a manner to compensate for said operating environment on said at least one micro-platform, and heat generated on the at least one micro-platform is distributed among the at least two circuit elements such that an effect of temperature drift is compensated.

Problems solved by technology

In their formulation, the resistance behavior is found to be highly non-linear, with little or no change in resistance for low power dissipation (below a certain threshold), and dramatically increased instability above a certain threshold.

This is usually considered to be a disadvantage for the use of polysilicon for resistive elements where stability is important.

This in turn requires high voltage and brings the danger of damage from electrostatic discharge (ESD).

Thus, a substantial amount of power is required to be dissipated to attain the trimming temperature.

Any other configuration, such as side-by-side and made from the same deposited layer, would require much higher power-dissipation in the heater-resistor, which in turn would require a higher supply voltage and would unduly heat the substrate.

This procedure is not reversible, and can be used only at the manufacturing stage (not practical for user- or field-trimming).

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