Patent GB-748487-A (GB)
Title: Electric signal translating devices utilizing semiconductive bodies
IPC: H03F3/16
Filed: 1952-08-12
Abstract: 748,487. Transistors. WESTERN ELECTRIC CO., Inc. Aug. 12, 1952 [Aug. 24, I951], No. 20252/52. Class 37. [Also in Group XL (c)] An electric signal translating device comprises a semi-conductor body having two rectifying connections (source and drain) reverse biased to a like polarity relative to a third (grid or gate) connection so that a space change region is established in the current path between the source and drain connections. Charge current flows from source to drain and is controlled by a " grid " electrode which modulates the current flow through the space charge region, or by a " gate " electrode which modulates the width of a conducting channel of extrinsic material. In such devices, the presence of a thin space charge region containing few holes or electrons results in intense electric fields so that injected charge carriers are accelerated to produce low transit times, and improved high-frequency performance. The space charge regions may be provided by the reverse biasing of a P-N junction or a metal semi-conductor contact. In Fig. 1, ohmic connections 13 and 14 are provided on the P and N portions of a germanium body 10 comprising a P-N junction J. Connection 14 serves as the drain and is biased positively so that a space charge region S is provided in the neighbourhood of the reverse biased junction J. A source electrode 15 having a rectifying contact engages the body 10 near junction J and is biased negatively to inject electrons into the space charge region which flow to the drain 14. The source bias is small relative to the drain bias. Input signals applied between the grid electrode 13 and source 15 result in output signals in load 19, both voltage and power gains being attainable. In Fig. 2, a slot 20 reaching almost to P-N junction J divides the N portion of the semi-conductor body into two portions 12A, 12B. The source comprises ohmic contact 150 on portion 12A, the drain ohmic contact 14 on portion 12B, and the grid electrode ohmic contact 13 on the P- type portion 11. Positive bias is applied to the source, and a larger positive bias to the drain, so that a space charge region S is formed around junction J, and electrons flow from source 150 to drain 14. Input signals may be applied between the source and grid electrodes, and amplified output signals taken from between the drain and grid electrodes. In Fig. 3, ohmic contacts 150 and 14 constituting source and drain electrodes respectively, are applied to the end portions of N-type zone 12 lying between P-type portions 11A, 11B, each of which has an ohmic contact 13A, 13B which are connected together to form the gate electrode. The source 150 has a positive bias, and the drain a larger positive bias so that a space charge region S forms around the two P-N junctions and in the neighbourhood of the drain electrode, thus providing a high output impedance. Potential variation between electrodes 150 and 13A, 13B results in variation of the width of the space charge layer, and thus of the impedance between electrodes 14 and 13A, 13B, to provide output signals. In one modification of this arrangement, the P and N portions are intercharged and the biases reversed, and in a further arrangement (Fig. 5, not shown) one of the two outside zones is omitted so that only one P-N junction is provided. In a further arrangement (Fig. 6, not shown) the source and drain electrodes both comprise point contacts engaging the surface of an N-type semi-conductor body. Both electrodes are biased in the reverse direction, the drain bias being greater than the source bias, so that a space charge region is formed around these electrodes, and holes flow from the source to the drain. The grid electrode consists of a metal plate on the opposite side of the body. The theoretical aspect of the invention is discussed, including the manner in which the space charge layer is formed around the drain electrode in arrangements like that of Fig. 3, and also the relationship between the reverse bias potential, the width and capacitance of the space charge layer, and the concentration gradients of the material. The necessity to operate with fields below that which introduces Zener current, and other factors are considered when deciding values of field strength and conductivity of the material. Fig. 9 shows an oscillator arrangement comprising a device similar to that of Fig. 2, having a tuned circuit connected between the drain 15 and grid electrode 13. Both source 14 and drain 15 electrodes are biased positively. The semi-conductor material may also consist of silicon copper oxide or lead sulphide. Reference is made to Specification 706,858 regarding the production of P-N junctions, and also to Specifications 694,021, 694,023, [Group XXXIX], 697,880, 700,321 and 700,236 regarding transistors.