Semiconductor testing instrument to determine safe operating area

1 . An instrument for determination of the dc safe area of operation of a semiconductor device-under-test comprises a first dc biaser to apply an adjustable dc bias at a first channel of a device-under-test, and a means to apply a bias signal at a second channel of a device-under-test which means comprises a second dc biaser to apply a dc bias at a bias point within the safe operating limit, and a variable biaser subsequently to apply a variable stimulus comprising fast, superimposed rectangular bipolar pulses, and wherein the instrument further comprises means to measure the current response thereto so as to permit extrapolation of a detailed I-V response in the vicinity of the safe operating limit.

2 . An instrument in accordance with claim 1 wherein the variable biaser generates pulses with progressively increasing amplitude.

3 . An instrument in accordance with claim 1 wherein the variable biaser generates a pulsed wave form that is essentially critically damped so as to achieve a minimum rise time up to the point where the pulses become substantially flat.

4 . An instrument in accordance with claim 1 wherein the variable biaser generates a pulsed wave form with a pulse length below about one μs.

5 . An instrument in accordance with claim 4 wherein the variable biaser generates a pulsed wave form with a pulse length below about 100 ns.

6 . An instrument in accordance with claim 1 wherein the means to apply the adjustable bias at the input comprises a high stability voltage source serially connected to the input via a resistor.

7 . A measuring instrument in accordance with claim 6 wherein the high stability voltage source is further serially connected through a low pass filter.

8 . A measuring instrument in accordance with claim 7 wherein the resistance is followed by a combination of series inductors and shunt capacitors to form the low pass filter.

9 . A measuring instrument in accordance with claim 1 , further comprising a remote head including at least the response measuring means, into which the device-under-test may be directly connected.

10 . A measuring instrument in accordance with claim 1 , further comprising a remote head including at least means to generate the superimposed fast, generally rectangular, synchronous bipolar pulses, into which the device-under-test may be directly connected.

11 . A method for determination of the dc safe area of operation of a semiconductor device-under-test comprising the steps of:

applying a dc bias at a first channel such as the input of the device-under-test;

applying a dc bias at a second channel such as the output of the device-under-test at a bias point base level within the safe operating limit of the device-under-test;

applying a variable stimulus at the second channel comprising superimposed fast rectangular bipolar pulses;

rapidly measuring the current response thereto at both the channels;

extrapolating from the responses a detailed I-V response for the device in the vicinity of the safe operating limit.

12 . A method in accordance with claim 11 wherein the variable bias is applied in the form of pulses with progressively increasing amplitude.

13 . A method for determination of the dc safe area of operation of a semiconductor device-under-test comprising the repeated performance of the steps in accordance with claim 11 as an iterative succession.

14 . A method in accordance with claim 13 comprising the steps of:

applying an initial dc bias at a point known to be well within the safe operating area of the device-under-test;

superimposing a pulsed bias and in particular a pulsed bias of progressively increased amplitude;

detecting incipient breakdown and removing the pulsed bias;

determining a second dc biasing point nearer to but safely below the breakdown point as identified hereinbefore;

repeating the process steps above until a sufficiently accurate characterisation of the breakdown point is obtained.