Patent GB-1453858-A (GB)
Title: Process and circuit arrangement for the adjustment of the per formance characteristics of an integrated circuit
IPC: H01L27/08
Filed: 1973-11-16
Abstract: 1453858 Adjusting integrated circuits ROBERT BOSCH GmbH 16 Nov 1973 [18 Nov 1972] 53187/73 Heading H1K A silicon s/c body 9 (Fig. 1) containing a monolithic integrated circuit has an in-diffused electrical resistor comprising four series partial resistors R 1  to R 4  forming part of the integrated circuit. A conductor track forming part of the conductor metallization of the circuit shorts out the series partial resistors R 2  to R 4  in corresponding sections M 2  to M 4  narrowed to necks S 2  to S 4 , and the net resistance is adjustable by selectively burning out the necks by a pulsed electric current. In construction (Fig. 2) a conductive layer 7 is diffused into the s/c substrate 6 in known manner, is overlain by an epitaxial layer 10, and an SiO 2  layer 8 is applied thereto. The resistor series comprising R 1  to R 4  is diffused into layer 10 through a window etched into layer 8 and subsequently closed. A conductor track of e.g. Al forming part of the normal metallized connections overlies layer 8 and contacts the intermediate points of the resistor series R 1  to R 4  through etched windows thereof; while comprising track sections M 2 , M 3 , M 4 . Section M 3  is opened by burning off the neck, to adjust the total value, and other values may be achieved e.g. by leaving all the short-circuits intact (Fig. 3, not shown) or burning out M 2 , M 4 , M 5  (Fig. 5, not shown) or burning out M 3  (Fig. 6, not shown), Numerical values are quoted, and the diffused resistor is replaceable by diodes or transistors. Selective burn out is achieved for the appropriate neck denoted by Si by the circuit of Fig. 7, wherein a voltage source 20 optionally supplies linear, stepped, and constant time function waveforms. A storage capacitor is charged over resistor 22 and is connected to collector 4 of switching transistor 23, whose emitter is connected over the turn out section while it is triggered by astable multivibrator 23 supplying rectangular base pulses of constant frequency and duration; or alternatively a signal having a time dependent frequency of constant pulse duration, or a time dependent pulse duration of constant frequency, or of time dependent frequency and pulse duration. A source of constant current is also applied to the burn out neck section Si. A Schmitt trigger 26 emits, with time lag or directly, a blocking pulse to a blocking input of pulse generator 24 when the resistance of Si reaches a predetermined value corresponding to interruption, so that no more pulses are applied thereto. The time lag may correspond to one further pulse. In a modification (Fig. 8, not shown) an inductive energy store is charged through the switching transistor and discharges through a free running diode; while the voltage source 20 may operate directly through the switching transistor (Fig. 9, not shown). The voltage source is replaceable by a current source bridged by the emitter-collector path of the switching transistor (Fig. 10, not shown). Burn out pulse sequences may comprise successive pulse groups of fixed duration and frequency progressively increasing in amplitude (Fig. 11, not shown) successive progressively increasing pulses (Fig. 12, not shown) group sequences of pulses of constant amplitudes and frequencies progressively increasing in width (Fig. 13, not shown) and successive pulses of constant amplitude and frequency progressively increasing in width (Fig. 14, not shown); and also a sequence of individual pulses of constant amplitude and width and decreasing frequency (Fig. 15, not shown) or a sequence of pulses of constant amplitude and width; increasing in amplitude; superimposed on a constant current (Fig. 16, not shown).