Patent GB-787426-A (GB)
Title: Improvements relating to semi-conductor devices
IPC: H01L29/00
Filed: 1954-03-18
Abstract: 787,426. Transistors. GENERAL ELECTRIC CO. March 18, 1954 [March 23, 1953], No. 7931/54. Class 37. [Also in Group XL (c)] A unipolar transistor comprises an elongated body of one conductivity type with a band of material of the opposite conductivity type extending around at least part of a cross-section of the body between its ends and ohmic electrodes on opposite sides of the band. The Fig. 2 embodiment comprises a body 2 of low conductivity N-type material with ohmic electrodes 14, 6 at opposite ends, with a closed band of high conductivity P-type material 3 formed round its periphery between the ends by diffusion from a layer of, e.g., In fused to it. The PN junction 4 thus formed is reverse biased to produce an annular region 8 adjacent the junction in the N body practically devoid of carriers and hence of high resistance. The extent of the region and thus the resistance between electrodes 6 and 14 is controlled by the value of fixed bias 5 and the instantaneous magnitude of the signal voltage from source 7 in series with it. If the load resistor 12 connected between the power supply and electrode 14 is comparable to the minimum resistance between electrodes 6 and 14 an amplified version of the input signal is obtained between point 15 and earth. To produce maximum amplification the part of the main body between the band and electrodes 6 and 14 should be as short and of as large cross section as convenient since its resistance is invariant. The resistance of the device varies non-linearly with the band bias voltage because the width of exhausted region increases as the square root of bias voltage and because the rate of change of cross-sectional area of the region varies with the instantaneous extent thereof. In Fig. 4 (not shown) two coplanar bands of P material each extend half-way round the periphery. Each is reverse biased and has a signal source in series with its bias supply. The change in the resistance of the device produced by a signal of fixed amplitude applied to one band depends on the bias and amplitude of the signal applied to the other band so that the device effectively multiplies the signals. This is because one signal operates to exhaust carriers from a region which would also be exhausted by signals applied to the other junction. Similar conditions govern the operation of a modulator device, Fig. 5 (not shown), which has two complete P-type bands in different planes so closely spaced that signals applied to them produce overlapping exhausted regions. If the bands are widely spaced so that no overlapping occurs the output is the sum of functions of the two separate inputs. In Fig. 6 is shown a device with two coplanar half bands 38, 40 and a closed band 42 in a different plane each with its own bias and signal sources. Depending on the spacing of band 42 from the other bands it is possible to make a device which multiplies all three signals, or one which adds a function of the product of the signals applied to bands 38, 40 to a function of the signal applied to band 42. In this case the voltage applied to band 42 may be used to vary the amplification of the circuit or to act as an on/off switch. Specifications 727,900 and 728,129 are referred to.