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Low Voltage Switching Resistor and Its Applications

IP.com Disclosure Number: IPCOM000048180D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 41K

Publishing Venue

IBM

Related People

Malaviya, SD: AUTHOR

Abstract

One of the techniques to permanently alter the value of a resistor on a chip is to first damage a part of it by ion implantation to increase its resistivity and then to heat it, such as by passing current through it, to anneal the damage, thereby permanently decreasing the resistance. Resistivity changes by several orders of magnitude are possible. The switching resistors are very useful for permanently changing the electrical state of any type of circuit.

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Low Voltage Switching Resistor and Its Applications

One of the techniques to permanently alter the value of a resistor on a chip is to first damage a part of it by ion implantation to increase its resistivity and then to heat it, such as by passing current through it, to anneal the damage, thereby permanently decreasing the resistance. Resistivity changes by several orders of magnitude are possible. The switching resistors are very useful for permanently changing the electrical state of any type of circuit.

A very valuable application of the switching resistor is in the implementation of redundancy on a memory chip. Any defective part of the circuit, such as a word or bit line decoder, sense amplifier, off-chip driver, etc., can be deactivated permanently by switching appropriate resistors of the circuit. Also, a spare or redundant circuit can be brought in to replace the deactivated faulty part electronically.

The circuit described herein enables the automatic steering of the resistor switching pulse to the selected location, making use of the normal decoders. The scheme also avoids overheating or electrically overstressing of the working components of the integrated circuit, thereby practically eliminating reliability risks. Also, the switching is done without the need for high voltage pulses which are almost invariably needed in the currently known circuit configurations. The need to redesign the bipolar process for high voltage is thus eliminated.

The example given below is for bipolar transistor technology. A similar scheme can be used for other technologies.

As shown in Fig. 1, the device consists of an NPN bipolar transistor formed within isolation regions 9 whose base 10 is extended on one side to accommodate two base contacts B1 and B2. A suitable implant, for example, Si or H+, is made into the base, between the two contacts, by opening a small window in the silicon dioxide 8 and silicon nitride layer 11 on top. A screen silicon dioxide is desired for the implant. Further passivation, for example, by polyimide, or silicon dioxide layers may then be used. It is preferred to confine the damage to within the base region to avoid junction leakage. However, a leaky junction can be taken care of by minimizing the voltage across it, for example, by tying one end, B1 or B2, of the base resistor to the collector, C. The emitter contact of the device is designated as E.

To switch the resistor, the bipolar device is turned on by applying a voltage V(be) across the emitter and B1. The collector is tied directly to a positive voltage supply V(cc). The high voltage, such as +1.5 to +5 volts, of the normal V(cc) generates heat at the subcollector 12 which in turn quickly reaches the implanted region of the base due to close proximity. The damage is thus annealed. This is in sharp contrast to the usual method of the prior art where the damaged part is heated by passing the current through the resistor itself. A high voltage pulse, about...