US2769926A

US2769926A - Non-linear resistance device

Info

Publication number: US2769926A
Application number: US341164A
Authority: US
Inventors: Israel A Lesk
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1953-03-09
Filing date: 1953-03-09
Publication date: 1956-11-06
Anticipated expiration: 1973-11-06
Also published as: FR70234E; FR68864E; FR1097337A; GB791959A; FR69038E; FR69037E; GB815468A; FR70427E; US2876355A; FR69265E; FR70235E; US2863045A; US2801340A; FR67158E; FR70233E; GB815296A; GB815361A; US2792499A; FR71345E; GB757536A

Description

Nov. 6, 1956 1. A. LESK 2,769,926

NONLINEAR RESISTANCE DEVICE Filed March 9, 1953 3 Sheets-Sheet 1 Fig?) IsraelALesk,

dwrfim His Attorney Nov. 6, 1956 A. LESK NON-LINEAR RESISTANCE DEVICE 3 Sheets-Sheet 2 Filed March 9, 19543 Inventor l'r'ael A.Le sk by His Attorney.

Nov. 6, 1956 I. A. LESK NON-LINEAR RESISTANCE DEVICE iled March 9, 1953 5 Sheets-Sheet 5 Inventor: lsraelAL'esk,

HisAttofney.

United States 2,7 69,926 N N JJN'EAK RESESTANCE DEVICE Application March 9, 1%3, Serial No. 341,164 9 Claims. (Cl. 307-385) This invention relates to non-linear resistance devices and more particularly to such devices formed of semi-- conductive material and to circuit arrangements utiliz ing such devices.

The theory of electric conduction in solids by means of holes and electrons, as it is presently understood, is assumed to be well known to those skilled in this art. Therefore, only a brief summary of so much of the theory as is thought necessary to understand the present invention will here :be presented.

As is well known, semiconductive materials are classitied as P-type semiconductive materials and N type semi conductive materials. The type of predominant activator material included in the semiconductive material determines the class into which the material falls.

jority activator in Isemiconductive materials, trons therefrom and thus create a deficiency of electrons in the vsemicond-uctive material. The spaces left by the electrons trapped by the acceptor activator are called holes and act as though they were mobile positivelycharged electrons. It can be said, therefiore, that in P-type semiconductive materials, conduction takes place with holes as positively-charged current carriers.

Donor activator materials, when present as the ma- If the P-type material is maintained at a positive potential relative to the N-type material, the holes in the P-type material are repelled from the positive potential and mi grate toward the N-type material under the influence of the electric field. The holes travel throughthe N-type neutralized by excess electrons in the N-typ'e material. Similarly, excess electrons from the N-type region migrate across the P-N junction into the is called forward bias.

If, however, the P-type material is biased negatively with respect to the N-type material, the holes in the P-type material and the excess electrons in the N-type material are attracted away from the" junction; Thus the area in the vicinity of the P-N junction is almost devoid of carriers and little current fl'ows. The small resulting current is caused by free holes and free electrons, created thermally, that migrate to the barrier region, travel across the junction, and combine with the excess carriers in the opposite region. This small resulting current is called- 2,769,926 Fatented Nov. 6, 1956 either NP-N or P-N-P junction transistors depending on joined. Both types of junction transistors exhibit similar properties and differ mainly in carrier types and in bias polarities required.

Conventional junction transistors, however, require two P-N junctions. Further, these junctions must be accurately positioned relatively to each other and must be separated by only a very small distance for optimum performance. As a result, junction transistors are very costly, ditficult to make, and further, require complex equipment in their manufacture.

Accordingly, it is an object of this invention to provide a semiconductor amplifying device utilizing only a single P-N junction.

Another object of this invention is to provide an improved semiconductor device that exhibits negative resistance characteristics.

A further object of this invention is toprovide a semi conductor device that is useful as a switching relay whereby a small amount of energy controls the flow of a large amount of energy.

The objects of my invention may be realized through the provision of a PN junction formed by a region of P-type semiconduc'tive material contiguous with a region of N-type semiconductive material, and means for biasing a portion of said junction in the forward directionand the remaining portion in the reverse direction.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself,

nection with the accompanying drawings wherein:

Pig. 1 is a plan view of a semiconductor device embodying the principles of t 's invention with the biasing circuits therefor schematically shown;

Fig. 2 is a front view of the device illustrated in Fig. 1;

Figs. 3-5 are front views of the device illustrated in Fig. 1, and show the charge distribution around the P-N junction for various relative voltage magnitudes;

Figs. 6-8 are graphs of voltage plotted against distance for various relative magnitudes of voltages and correspond to the charge distribution as shown in Figs. 35 respectively;

Fig. 9 is a graph of voltage versus current for the device shown in Fig. 1;

Fig. 10 is a schematic circuit diagram of a relay utilizing. the semiconductor device shown in Fig. 1, and

Fig. 11 is a schematic circuit diagram showing a modification of the relay illustrated in Fig. 10.

Referring to Fig. 1, a semiconductor device, designated comprises an elongated single crystal bar 12 of any suitab e N-type semiconductivematerial such pellet 23 of an acceptor activator material such as indium is located at the'approximate midpoint of one face of the bar 12.

During manufacture, the dot 23 is heated and a portion of the acceptor activator material is fused into the bar 12. Although there are donor activators present in the material, sufficient acceptor activator fuses into the semiconductive material so that acceptor activators predominate and a region 25 (Fig. 2) below the dot 23 becomes a P-type semiconductor region. Thus a rectifying P-N junction as indicated at 27 exists in the bar 12. The method of producing such a PN junction is not in itself a part of this invention. Suitable methods of, and apparatus for, the construction thereof are disclosed and claimed in a copending application of William C. Dunlap, Jr., Serial No. 187,490, filed September 29, 1950, now abandoned, and assigned to the assignee of the present application.

As shown in Fig. l, the bar 12 is composed of N-type semiconductive material and the dot 23 is composed of acceptor activator material. The same performance characteristics are obtained, however, if the dot 23 is donor activator material and the bar 12 is P-type semiconductive material. The only change necessary is a reversal of the polarity of the bias voltage sources to be described.

A suitable source of direct voltage, here indicated by the battery 21, is connected to the

conductors

17 and 19 to establish a unidirectional potential along the longitudinal axis of the bar 12. As shown in'Figs. 6-8, a potential gradient exists in the bar 12, the potential having its minimum value at one end of the bar 12 and its maximum value at the opposite end. Another source of bias voltage, here shown as a battery 29, is connected between the dot 23 and the ohmic nonrectifying contact 13 by

conductors

31 and 33. The battery 29 can be connected between either

ohmic contact

17 or 19, all that is required is that terminal of the battery 29 that is connected to the

contact

13 or 15 be of the same polarity as the terminal of the battery 21 that is connected to the same contact.

The range of values of the voltage of battery 29 is critical and its magnitude relative to the magnitude of the voltage of battery 21 is determinative of the negative resistance characteristics of the device 11, as will appear.

The effects of various magnitudes of bias voltage on the device 11 can best be understood by reference to Figs. 3-5 wherein the battery 29 is replaced by a variable voltagesource such as a variable battery 35.

In the following discussion it is assumed that the side of the P-N junction to which Va is connected, here shown as a dot 23, is equipotential. This is essentially true in practice since the dot 23 is made of a good electrically conducting material.

In referring to Figs. 3-5, and in correlating them'to Figs. 6-8, the left-hand end of the bar 12, which is connected to the negative terminals of

batteries

21 and 35, is considered as a reference point of zero voltage.

Attention is first directed to the circuit illustrated by Fig. 3 wherein the value of the voltage derived from battery 35 is adjusted to a value much greater than one-half the magnitude of the voltage impressed by battery 21 along the longitudinal axis of bar 12. For this relation of voltages, the P-type region 25 is positive relative to the N-type region immediately below the junction 27 because the voltage impressed in P-type region 25 from battery 35 is positive and is greater than the positive voltage existing in the bar 12 at all points below the junction 27 due to the battery 21. This is a forward bias for the junction 27 and the area of the entire junction 27 consequently emits holes.

Fig. 6 shows a graph of the voltage along the longitudinal axis of the bar 12 plotted against the distance along the bar 12 as measured from the left end thereof. The non-linearity results from the flow of current into the bar 12 from the junction 27. As can be seen from Fig. 6, the voltage applied to the dot 23, V0, is considerably greater than one-half the magnitude V0 of voltage applied to the length of bar 12.

In the circuit shown in Fig. 4, the value of the voltage 'c of battery 35 is decreased to a magnitude considerably smaller than one-half the magnitude of the voltage applied to the length of the bar 12, V0. For this relation of V0 to V0, the junction 27 is biased in the reverse direction over its entire area because the region of P-type semiconductive material 25 is negative relative to the voltage of the area of the bar 12 directly beneath the junction 27. This reverse bias prevents hole current flow into the body of N-type semiconductor, and space charge collects along side of the junction barrier. The entire area of the junc tion 27 thus is biased in the reverse direction. This condition is illustrated by the graph of Fig. 7 in which the relation between voltage and distance along the bar 12 is shown as being linear.

In the circuit shown in Fig. 5, the value of the voltage derived from battery 35 is approximately equal to one-half the magnitude of the voltage of battery 21. When this voltage relationship exists, the potential of the P-type semiconductive region 25 is intermediate the values of the potentials of the N-type semiconductive region adjacent it. Thus, because of the potential gradient existing in the bar 12, the value of the voltage at the left side of the P-type region 25 is greater than the voltage of an N-type semiconductive region 37 adjacent it. In this area 37, therefore, the N-type region is negative with respect to the P-type region 25 and the left side of the junction 27 acts as an emitter, i. e. is biased in the forward direction. This is indicated in Fig. 5, by the lack of accumulated space charge in the area 37 of the junction 27.

However, the voltage V0 applied to the dot 23 is less than the voltage existing in a N-type region 39 adjacent the right side of the P-type semiconductive region 25. Since the voltage V0 is less than the potential existing in the N-type region 39 of the bar 12, the junction of the N-type region 39 and the P-type region 25 is biased in the reverse direction, i. e. as a collector.

Therefore, when the value of the voltage Vc applied to the dot 23 is intermediate the value of voltage existing in the bar 12 at the sides of the region 25, the N-type region 37 and the P-type region 25 form an emitter junction and the N-type region 39 and the P-type region 25 form a collector junction. When this condition exists, the relation between current Ic flowing through the junction 27 and the voltage V0, applied between the dot 23 and the contact 13, exhibits non-linear properties including a negative resistance region. Fig. 9 shows a graph of this current-voltage relation. The region AC of the voltage-current curve is the negative resistance region. Because of this negative resistance region, a small increase in voltage from a value of C to a value of C+AC causes a current increase from the value C to the current value at point B. Thus, the device 11 is extremely sensitive to a small change in voltage and is adapted to relay operation.

Fig. 10 shows a relay circuit utilizing the semiconductor device 11. As in Fig. l, the battery 21 establishes a unidirectional potential across the bar 12. The magnitude Vc, the potential of battery 29, is set at a value slightly less than C (Fig. 9), and a coil 41 of a marginal relay 43 is connected in series with the battery 29. The marginal relay 43 is adjusted so that it is insensitive to the normal flow of current through the coil 41. A source of controlling voltage 45 is connected to terminals 47 and 49 in series with the battery 29 so that the voltages are additive.

When a controlling voltage pulse V is applied to the terminals 47- and 49 from the source 45, the pulse voltage adds to the voltage Vc and because of the negative resistance region AC (Fig. 9) a rapid increase of currents occurs, the magnitude of current changing from the value at point C to the value at point B. This electrical contact between

terminals

51 and 52. As a result of the shorting of

terminals

51 and 52, current from a source of potential 55 flows, through a device to be controlled 57 thereby energizing it. If desired, the normally open marginal relay .3. can be replaced by a normally closed relay, the only difference being that contact is broken instead of made when the current flowing through coil 41 increases.

Fig. 11 illustrates a modification of the circuit shown in Fig. 10. In this modification the controlling voltage pulse Vp from source 45 is applied to terminals 5-9 and 61, the polarity of Vp being as shown and is such as to subtract from the voltage V0 of battery 21. When a controlling pulse is impressed between terminals 59 and 61, the voltage between contacts 13 and of the device 11 is decreased. This decrease in voltage lowers the value of the unidirectional field in device 11 to a point where the voltage Va is intermediate the values of axial voltage at the sides of dot 23. As previously explained this .condition results in a negative resistance characteristic for the current flowing through the dot 23. Therefore, the current increases from a value near point C (Fig. 9) to a value near point B and thus operates marginal relay 43 as explained in the discussion of Fig. 10. Because the curve of Fig. 9 is drawn for a particular value of V0, the exact currents flowing through the device it will not be equal to the values at point C or B. The curve will be displaced slightly because the value of the voltage applied between

contacts

13 and 15 is changed by the amount of the controlling voltage V The negative resistance region AC (Fig. 9) indicates that, as the current increases, the voltage decreases. A physical explanation of this negative resistance region lies in the fact that, when minority carriers are injected into a semiconductive material having majority carriers, the resistance of the semiconductive material may be appreciably lowered. This is especially true of high resistivity semiconductive materials. Since V=RI if I increases, the voltage will decrease only if the percentage decrease in R is greater than the percentage increase in I.

When any part of junction 27 becomes biased in forward direction, holes are emitted from the P-type region 25 into the l-type region. These injected holes appreciably lower the resistance of the bar 12, especially in the region between the dot 23 and the ohmic contact 13. To obtain the negative resistance region AC it is necessary that the quantity of semiconductive material into which the holes are injected be small. Otherwise the holes injected into the bar 12 do not lower the resistance to the required degree because there are only relatively few holes to change the resistance of a large quantity of semiconductive material. If, however, the total amount of semiconductive material is small, the holes injected into the material cause a change in resistance of the semi-conductive bar 12 between the dot 23 and ohmic contact 17 that is appreciable with respect to the original resistance of this region of the bar 12, and thus as the number of holes injected into the bar 12 increase, that is, the current increases, the resistance of the bar 12 decreases by a larger percentage, thus creating the negative resistance region A-C.

In an operative embodiment of this device the value of V0 is approximately 22 /2 volts, and the dimensions of the bar 12 are approximately .2 inch long by .1 inch wide by .01 inch thick.

The range of values of Va relative to V0 that gives the negative resistance region A-C of the voltage current curve is herein described as being distributed around a voltage approximately equal to one-half the value of V0. However, if the dot 23 is placed other than at the midpoint of the bar 12, the same results are obtained ut with diii rent r l i m g itudes of Va and V0. Such a figura i n i within he contempla ion of the present invention.

l ho gh y in nt n. ha be n des rib above in nne ion with pec fi em d m n s, many mod fications may be made. It is to be understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the U. S. is:

l. A semiconductor device comprising a body of semiconuctive material having conduction car e of o type predominating, a region of said body having conduction carriers of the other type predominating and with n sai b dy, a e tr e n- 7 and spaced from said junction, means electric field in said means for establishing a pois intermediate the, potentials away from said electrode, tential at said region which junction and the one of said electrodes toward which injected carriers move being sufficiently small that the resistivity thereof is appreciably changed by injection of greater than said predetermined value which varies directly with current flow.

between said electrodes, means for establishing a poten- 4 In combination, a body of semiconductive material having conduction carriers of one conductivity type predominating and having a pair of spaced electrodes thereon, a load circuit, means for applying a potential between said electrodes through said load circuit, and means for controlling the current in said load circuit by minority carrier injection comprising an input circuit connected between one of said two electrodes and the region of injection, said region of injection being located on said body between said electrodes and having conduction carriers of the opposite type predominating, said region being biased at a potential intermediate the potentials at said electrodes.

5. In combination, a body of semiconductive material having conduction carriers of one conductivity type predominating and having a pair of spaced electrodes thereon, means for applying a potential between said electrodes, means for controlling the current flow between said electrodes by minority carrier injection comprising a region having conduction carriers of opposite type predominating, said region being spaced on said body between said electrodes and being biased at a potential lying between the potentials at said electrodes.

6. In combination, a semiconducting body having a pair of base electrodes embracing a region of uniform conductivity type, means for applying an electric potential between said base electrodes, an additional electrode making rectifier contact with said body at a region within the electric gradient produced by a diflerence in potential between said base electrodes, and an electric circuit connected between said additional electrode and one of said base electrodes and having impedance elements causing the potential of said additional electrode to lie within the potential range spanned by said base electrodes.

7. In combination, a semiconducting body of uniform conductivity type having a pair of base electrodes spaced at opposite ends of said body, means for applying an electric potential between said base electrodes, an additional electrode making a rectifier contact with said body, and means biasing said additional electrode to potentials within the range spanned by said base electrodes.

8. A semiconductor device comprising a body of semi conductive material of one conductivity type having a pair of spaced contacts thereon, a region of another conductivity type in said body intermediate said contacts and forming a junction within said body, means for applying a potential between said contacts, means for applying a potential to said region which is intermediate the potential at said contacts, the distance between said junction and that one of said ohmic contacts toward which injected carriers are attracted being sufliciently small that the resistivity of that portion of said body of one type conductivity included therebetween is changed appreciably by injection therein of minority carriers from said region, the change in voltage between said region and said one contact varying inversely with the change in current flow therebetween.

9. A semiconductor device comprising a bar of semiconductive material of one conductivity type having first and second ohmic contacts at opposite ends thereof, and a region of opposite conductivity type intermediate said ohmic contacts forming a P-N junction with said bar, means for applying a potential between said ohmic contacts, means for applying a potential to said region with respect to one of said contacts which is intermediate the potentials at the ends of said bar.

References Cited in the tile of this patent UNITED STATES PATENTS