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Method and System for Accommodating Variations in Resistance in a Circuit

IP.com Disclosure Number: IPCOM000202031D
Publication Date: 2010-Dec-01
Document File: 3 page(s) / 114K

Publishing Venue

The IP.com Prior Art Database

Abstract

A method and system for accommodating variations in resistance in a circuit is disclosed.

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This is the abbreviated version, containing approximately 51% of the total text.

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Method and System for Accommodating Variations in Resistance in a Circuit

Disclosed is a method and system for accommodating variations in resistance in a circuit.

Thin-film resistors are extensively used in microchips. The thin-film resistors are generally composed of silicided polysilicon, polysilicon, diffused silicon, and refractory metal layers such as TiN or TaN, or very thin metal layers. A thin-film resistor that is composed of physically deposited metals has a sheet resistance that may be controlled within tolerance limits of 5% of a target resistance value. This is due to the accuracy of crystal monitors used for deposition of the film. However, polysilicon based thin-film resistors and diffused Si thin-film resistors have greater variability in resistance value. The resistance value depends on implant tolerances and subsequent thermal treatment of the deposited film. Further, the resistance value in this case also depends on the thermal treatment that is performed in order to activate the implanted species. Accordingly, polysilicon based thin-film resistors and diffused Si thin-film resistors have twice the variability in resistance values when compared to thin film metal resistors. In both the cases, circuit designs require accurate resistors that are capable of maintaining resistance values within a specific tolerance limit of resistance over the lifetime of the circuits.

However, the resistance values of these resistors vary with time and the variation is based on temperature and current. In addition to the variation due to temperature and current, additional variation is caused due to the fabrication processes used. Thus, the final variation causes the resistance value to exceed the tolerance limits for the circuit and causes premature failure of the circuit. Further, circuits have varying distances between contacts (wire bond and solder bump). This variation in distance further causes variation in the resistance.

The method and system disclosed herein uses a resistor layout scheme with the ability to reduce the resistance value of a circuit to a pre-defined value and maintain the resistance value within tolerance limits. Reduction in the resistance value may be achieved by using FETs. Alternatively, fuses may be used to add or remove resistor components of a resistor.

For example, resistor components may be removed from a resistor layout illustrated in Fig. 1 with three resistor components R1 , R2 , and R3 . Each component is connected to a different metal level, i...