DE1005193B - Method of manufacturing crystal rectifiers with negative resistance - Google Patents

Description

Method of making crystal rectifiers with negative Resistance The invention relates to a method for producing electrical Crystal rectifiers, d. H. of rectifiers made of a body or crystal made of suitable semiconducting material and generally with a needle electrode are provided, which is in point contact with the surface of the semiconductor. the rectifying electrode can also consist of a metal film, the one takes up very little space on the crystal surface.

The invention relates to a manufacturing method for crystal rectifiers with negative resistance, which is suitable for bistable multivibrators and the for repeated tripping at very high frequencies or extremely short electrical ones Impulse is suitable.

It has long been known to use silicon, germanium in crystal rectifiers or to use certain other semiconducting substances that have a negative effect Resistance arise when they are in the reverse direction or in the direction of high resistance be polarized: You can therefore build bistable multivibrators be used. Examples of trip circuits of this type are e.g. B, in the British Patent 650,007.

Such flip-flops with germanium crystals cannot, however triggered repeatedly at frequencies higher than 31IHz. That will in general attributed to a thermal effect on the contact, which is a limiting "leading constant caused.

According to the method, however, germanium point contact rectifiers so constructed and electrically formed or treated that in the transmission characteristic of the rectifier one or more areas of negative resistance occur.

This means that the rectifier is in bistable multivibrators works in the forward direction and that then the limiting time constant is essential is less because the above-mentioned thermal effect does not occur. In this way Trigger frequencies up to at least 40 '\ -IHz can be used, and one Number of such flip-flops that work as binary counters can be stable at an input frequency of at least 13.5 MHz.

The method according to the invention for making point contact crystal rectifiers negative resistance in which an N-type body is used as a semiconductor and the material of the point contact electrode small additions of the donor type contains and is formed by means of a short-term current, is characterized by that the conditions of electrical formation, such as current strength, pulse duration, number of pulses etc., are chosen so that the current-voltage characteristic is in the forward direction Has an area with a negative slope.

The invention also relates to rectifiers according to this Method.

In a further embodiment of the invention, a method for electrical Formation of N-type semiconducting material provided with a base electrode is that in contact of low resistance with part of the surface of the semiconductor stands, suggested. This is the exposed surface of the semiconductor material subjected to an etching process and on the etched surface with a rectifying Provided an electrode made of a material which is a donor impurity contains. This rectifying contact is used for electrical formation briefly a current in the direction of passage or in the direction of low resistance of such strength that the current-voltage characteristic of the rectifying Contact receives at least one area with negative resistance.

With linpulszeitinodulation, the number of channels that have one transmit a single message line can be, by the frequency level limited. There is great difficulty in finding suitable equipment for generating the Construct high frequency and its reception.

With rectifiers constructed in accordance with the present invention and are electroformed, but can impulse systems with about 1000 conversation channels be built.

There are already methods of manufacturing semiconductor devices with point contacts known in which N-type semiconductor material and needle electrodes with donor-type additives and the semiconductor devices with a short-term current can be formed. An area with negative Slope can be obtained. It is true that such semiconductor devices can also be in bistable Flip-flops are used, however, the usable amperage is due to the Utilization of the locking characteristic, in contrast to those produced according to the invention Devices, only very few.

It was also found that germanium rectifiers were manufactured that have a negative resistance range in the continuity characteristic exhibit when exposed to vibrations from 3000 to 30000 MHz, e.g. B. on the order of 10,000 MHz. These can be excited to vibrate at frequencies that are smaller than those of the applied vibrations. The area However, negative resistance disappears when the applied oscillations are switched off will.

By building and treating according to the method, the rectifier becomes given an area of negative resistance in the continuity characteristic that is independent of the presence of any external vibrations and in his original expansion remains.

The method is to be explained in more detail with reference to the drawings will.

Fig. 1 shows details of a circuit for electrical formation a crystal rectifier according to the invention and for observing the characteristic this rectifier; Figs. 2 and 3 show curves showing the through-current-voltage characteristic of the rectifier after electrical formation according to the invention.

Rectifiers with negative resistance in the continuity characteristic preferably made as follows: A piece or crystal of N-type germanium is provided in a known manner with a base electrode on part of the surface, which is in non-rectifying contact of low resistance therewith.

Another part of the surface is sanded and polished and becomes etched on it, e.g. B. with one of the usual etching solutions, the hydrofluoric acid, nitric acid and copper nitrate. However, other suitable etching solutions can also be used will. The needle electrode or the rectifying electrode should be made of one material which contains a small amount of donor impurities. It can z. B. silver or copper with a small amount of arsenic or phosphorus is used will. Most advantageous, however, is silver with about 1/10% arsenic. It can a different ratio can also be used, but 1% of the additive is that Maximum which is still suitable for the present case. The needle electrode is in contact with the germanium crystal surface in some known manner arranged and then forms a germanium rectifier with more or less common Curve. To obtain an area of negative resistance in the continuity characteristic, an electroforming process described with reference to FIG. 1 is used shall be.

In Fig. 1, the rectifier consists of a crystal or body 1 of rectifying material, preferably of germanium, with a metal base plate 2 is well connected by soldering or another electrically conductive bonding agent, so that the connection point has a low contact resistance. The upper Surface 3 is preferably suitably etched using a Etching solution as mentioned above.

A needle electrode 4, preferably made of silver with 0.1% arsenic, is available in contact with the etched surface 3. The rectifier described so far is of a known type and has the usual rectifier characteristic.

The electroforming circuit connected to the rectifier exists from a power source 5. the z. B. AC current of 50 Hz at a voltage of 40 V supplies and is connected to electrodes 2 and 4 of the rectifier, in series with any current meter 6, the normally open contact 7 of relay 8 and a variable resistor 9. A capacitor 11 and a Switches 10, which are connected in series, are parallel to the two electrodes 2 and 4 of the rectifier switched on. The switch 10 is normally open, but it is closed when key 15 is pressed. A charging capacitor 12 is normally supplied by the DC power source 13 via a variable resistor 14 and the top contact of button 15 is charged, which is normally the circuit with the upper end of the capacitor 12 closes. One end of the relay winding 8 is connected to the lower contact of the button 15, while the other end is connected to the lower end of the capacitor 12. When the button is pressed is, the capacitor 12 is discharged through the relay winding, so that the Contact 7 is closed and a forming current through the rectifying contact flows between the needle 4 and the rectifier crystal 1. When the power source 5 is an AC power source, the through current through the rectifying Contact can be much larger than the reverse current. The through current can by means of the Resistor 9 can be set to a relatively large value, approximately between 0.76 and 2.5 A. The much smaller reverse current has no noticeable influence.

For better observation of the formation process, the rectifier characteristic imaged on a cathode ray tube. For the sake of clarity, only the deflector plates 16, 17, 18 and 19 of the oscilloscope are shown. The resistance 20 is connected between the electrode 2 of the rectifier and earth, and is on Tapping from this resistor is connected to the vertical baffle 18. The AC power source 21 is connected to one terminal to earth with the other connection via a blocking capacitor 22 to the electrode 4 of the rectifier connected and also to the horizontal baffle 17. The plate 16 is connected to the electrode 2, and the plate 19 is connected to earth. the horizontal deflection of the Cathode ray is accordingly the potential proportional to the rectifier, the vertical deflection is proportional to the current, which flows through the rectifier contact.

If the power source 5 is a direct current source, it must be more positive Pole to be connected to the electrode if it is assumed that the semiconductor material N-type is used for the rectifier.

When the button 15 is pressed, the capacitor 12 is over the Winding of the relay 8 discharged, and this attracts the armature, so that the contact 7 is closed. A forming current now flows for a very short time through the rectifying contact. By appropriately setting the capacity of the Charging capacitor 12, the time can be set during which the contact 7 remains closed. When the power key is opened again, the capacitor will 12 is recharged, and when the power key is closed again, the Forming current again through the rectifying contact. This process can can be repeated as often as required.

The usual rectifier characteristic is obtained before formation, in which the current rises continuously from zero and has a resistance in the forward direction which, within certain limits, decreases progressively as the voltage increases. If the rectifier is correctly formed, a loop is created in the curve, which characterizes a certain current range that is not stable in the rectifier can be sustained. This loop arises as a result of presence an area of negative resistance in the characteristic.

To create this loop in the curve, the power key 15 are operated more often. During the passage of formation current, a certain amount of heat generated, and if the rectifier using a If the needle electrode has been sufficiently formed from silver, then the needle is generally afterwards welded to the germanium surface. That's quite an advantage because the The needle electrode is held in place, and the characteristic curve of the formed Rectifier remains stable.

Strong high voltage surges with an exposure time of less than 1/10 microseconds bring the negative resistance created by the formation process to disappear again. That is why the capacitor is in the forming circuit 11 and the switch 10 are arranged so that no high voltage vibrations are generated can be if the circuit is interrupted by the contact 7 and this High-voltage oscillations cannot reach the rectifier in this way. In the other In this case, the loop generated in the characteristic curve would easily disappear again.

The loop in the curve, which corresponds to the unstable area of the formed Contact, is at a bias voltage of 1 to 15 V in the direction of passage achieved. The current associated with the lower break point of the loop has a value of a few milliamperes, e.g. B. from 100 - illiampere, depending on what is used for a formation stream. The discontinuous change of current in the loop of the curve is generally about 10 milliamps, often still more.

In most cases the current difference and voltage is the the loop corresponds roughly to the difference in power between the two Corresponds to the kink points of the loop, is approximately 2/3 W.

If the rectifier is sufficiently formed, it is advantageous to it in an insulating tube made of hardened plastic or in a cement or in Embed wax to protect it from moisture and mechanical influences.

It should be added that with a relatively small weld joint the needle electrode is separated from the formed germanium surface without destruction can be. In this case, the same needle electrode can again be applied to the welding point be attached or another needle can be used (e.g. from a other metal such as tungsten and not donor or other impurities contains), and one observes that the rectifier still has its new characteristic maintains.

This characteristic curve is applied to the superposition of several N and P layers that are in or near the surface of the crystal, however, the invention is independent of any theoretical explanation. It was further found that the area of the surface near the contact point, the shows the negative resistance is approximately 0.00625 mm in diameter.

If a needle electrode is made of any metal in this area the germanium surface is put on, the loop becomes in the continuity dividing line obtain. If the needle electrode is brought outside of this area, it disappears the loop instantly.

It should also be pointed out that the characteristic of the rectifier in the area of negative resistance usually, but not always, that is only two different, stable current values can be obtained if the load resistance, which is connected in series with the rectifier does not exceed a value, which is determined by the negative slope of the characteristic. This limit can z. B. be a few hundred ohms.

During the electroforming process, it is desirable that the generated Keeping the heat that forms at the point contact as low as possible by using one z. B. the germanium crystal mounted on a massive metal plate, which is still can be provided with cooling devices. It is also indicated, always for a few moments to wait after having let the forming current flow through the rectifier, to let the crystal cool down in the meantime. The width of the loop and hers The location depends to a certain extent on the temperature of the crystal. Also will the characteristic curve should therefore only be observed after the crystal has cooled down.

When you see the point contact during the forming process under the microscope If you look at it, you can see small sparks at the point of contact with the needle. These sparks have a bad influence on the characteristic. You can be prevented by z. B. a drop of suitable pure oil on the rectifying electrode at the point of contact when it is in contact with the crystal. This diminishes the distance around the needle where the sparks can occur and prevents that These sparks become visible. The sparks are also represented by the one shown in FIG Capacitor 11 reduced to a minimum, which is parallel to the during formation Rectifier can be switched.

In some cases one observes that the characteristic curve after the electrical Formation two or has multiple loops. They take place corresponding to the different through voltages. The curve between the Grinding is continuous. But there can also be different separate areas negative resistance occur, which correspond to the individual loops.

The best results of the procedure were with germanium crystals of the N-type and obtained with a silver contact needle with approximately 0.1% arsenic. this however, they are not the only materials that make up a rectifier with areas negative resistance can be produced in the continuity characteristic. For example Instead of silver, copper can be used as the material for the needle electrode In addition to arsenic, other impurities can also be found in the material of the needle electrode be added.

The welding of the needle in electroforming is also not an essential feature of the invention, but it has been found that the welding usually associated with adequate formation.

Crystal rectifiers that in the way they are in terms of the 1, show two different types of throughput characteristics. If the characteristic is of the type shown in FIG. 2, a The tilting effect is only achieved when there is a load resistance with the rectifier is connected in series, the value of which is smaller than the resistance, which corresponds to the negative slope of the characteristic. If the characteristic is of the type is, as it is shown in Fig.3, can have a tilting effect with any Load resistance can be achieved. Fig. 3 is the result of complex conditions, wherein the needle electrode simultaneously has several separate rectifying contacts with the crystal, at least one of which has a normal passage characteristic Has.

In Fig. 2, the voltage is plotted on the abscissa in the forward direction, which is connected to electrodes 2 and 4 of the rectifier (Fig. 1). The ordinate represents represents the associated current flowing through the rectifier. In this case it will consider a simple rectifying contact which, as described above, is electrical was formed. The curve starts at zero, and the first part, which is labeled 23 corresponds to the normal, positive resistance, which decreases with increasing current will. A reversal point 24 is then reached at which the resistance becomes negative. The rectifier characteristic then runs after the curve part 25 with negative resistance. As the current continues to rise, the voltage across the rectifier will drop by up to one second reversal point 26, at which the curve branch 27 is again with positive resistance connects. The part 27 again approaches the usual throughput characteristic, the denoted by 28 and shown in phantom in FIG. A continuity characteristic, like it represents the curve 28, the rectifier has before the electrical formation. When the rectifier receives a bias, that of curve 23 is close to the reversal point 24 corresponds, a small additional voltage causes the current to suddenly increases to a value which corresponds to a point on the curve branch 27, wherein still has to be taken into account that the load resistance that comes with the rectifier is connected in series, is not greater than the resistance caused by the Area 25 is characterized with a negative slope. A negative created as a result Voltage then causes the current to suddenly drop to the original low Value drops. So can the rectifier when it is in a suitable circuit is switched on, can be used as a bistable tilting device.

The characteristic shown in Fig. 2 can be viewed on the oscilloscope screen to be observed. It can be seen that in the case in which the resistor 20 of Fig. 1 shows the value of the negative resistance, which is indicated by the curve part 25 in Fig. 2, the curve 28: is obtained. When the resistance less than. is the negative resistance, the curve shows on the oscilloscope screen a loop.

The straight line 29 represents the load on the resistor 20 for the latter case when the voltage supplied by the current source 21 has the value V, where: the line 29 is the abscissa! tailors. The line 29 represents the relationship between the. Current flowing through resistor 20 and the difference Vv, where v is the potential drop across resistor 20U. The: Voltage 1-v is that which is applied to electrodes 2 and 4 of the rectifier. As the voltage V of the current source 21 varies, the line 29 is shifted parallel to the voltage axis, but the slope remains constant.

The: points at which line 29 intersects the rectifier characteristic, represent the possible current values, but each point is on the branch 25 of the curve unstable, so that the current only ever assume one or the other possible value can..

The dashed lines 30 and 31 are parallel to the line 29 and have their starting point at the reversal points 24 and 26. When the voltage of the current source 21 (FIG. 1) increases from 0, the part 23 of the curve appears on the oscilloscope until the reversal point 24 is reached, whereupon the electron beam jumps along the dashed line 30 to the point 32 and then follows the part 27 of the curve. If the applied voltage is now reduced, the curve part 27 is lengthened to the reversal point 26, and the electron beam jumps along the dashed line 31 to the point 33 and now follows the curve branch 23 to the zero point. Lines 30 and 31 are crossed so quickly that they cannot be seen on the oscilloscope screen, and since only parts 23 and 27 can be seen, there is a break between the two.

Fig. 2 shows the characteristic of a single, rectifying contact after electroforming in the manner described. When the needle electrode 4 (Fig. 1), however, produces two rectifying contacts, one of which is a normal Has continuity characteristic, so is the characteristic of the two connected in parallel Contacts as shown in FIG. The curve 34, 26, 24 is the passage characteristic of an electroformed contact and corresponds to the curve shown in FIG is. The curve 35 represents the passage characteristic of a normal, rectifying And the curve 36, 38, 37 is the continuity characteristic for two parallel switched contacts and is obtained by adding the ordinates of the two curves 34 and 35. The curve 36 has a more pronounced Z-shape than the curve 34, and the The current value of the first reversal point 37 (corresponding to point 24) is now higher than that of the second reversal point 38 (corresponding to point 26), instead of as in Fig. 2, is lower. For this reason, the curve branch 39 is between the Reversal points 37 and 38 always represent an unstable state, no matter how great the value of the resistor 20 may also be. You can see that the load line is always can be drawn so that it intersects curve 36 in three points, how big also their inclination is always (which must normally be negative). this is not possible in Fig. 2 when the load line 29 has a slope that is less than that of the curve branch 25 is. In Fig. 3, the extreme case is an infinite one Load resistance represented by the two dashed lines 39 and 40, which run parallel to the stress axis to the reversal points 37 and 38. In this Case, the curve appearing on the oscilloscope consists of two parts, the are separated by a gap.

It should also be pointed out that the curve 36 is a small one Contains area with negative slope afterwards at each reversal point, whereas the part of the curve between the reversal points has a positive slope.

The crystal rectifiers produced by the process can can be used advantageously for electrical trip circuits. Since the area with negative slope in the forward direction of the current-voltage characteristic, the currents occurring in the flip-flop are much larger than in the known devices. Also the use of the crystal rectifier according to Invention in binary electronic counting devices offers particular advantages. The frequencies used are in all cases only through the Circuit, but not limited by the rectifier. It can e.g. B. higher Frequencies than 40 MHz are used.

Although the invention for rectifiers with Nadelele :: electrodes described however, the needle electrode can be replaced with a metal film electrode covering the electroformed area and appropriately placed on the Surface of the crystal is attached, as is already known or suggested became.

It must be pointed out, however, that the polarization voltage, which puts the rectifier in the area of negative resistance, just a few Volts and that the associated current is generally the strength of a few Has mini amps. The power that the rectifier acts as a tripping device for consume two states or as an electronic counter is very low and can be supplied by a few cells in a dry cell battery. The arrangement is therefore particularly suitable for portable devices.

However, the above description represents only one exemplary embodiment and is not intended to imply any limitation on the concept of the invention.

Claims (11)

CLAIMS: 1. Method of making point contact crystal rectifiers negative resistance in which an N-type body is used as a semiconductor and the material of the point contact electrode contains small additions of the donor type and is formed by means of a brief current, characterized in that the conditions of electrical formation, such as current strength, pulse duration, number of pulses etc., are chosen so that the current-voltage characteristic is in the forward direction Has an area with a negative slope. 2. Process for the manufacture of crystal rectifiers according to claim 1, characterized in that the rectifying electrode on one Part of the semiconductor is applied, which has been subjected to an etching. 3. Procedure for the production of crystal rectifiers according to claim 1 or 2, characterized in that that the strength of the current used for electrical formation is between 0.75 and 2.5 amps. 4. Process for the manufacture of crystal rectifiers according to Claim 1 to 3, characterized in that a rectifying electrode Metal is used, which is when passing the formation current with the Welded surface of the semiconductor body. 5. Process for the manufacture of crystal rectifiers according to claim 4, characterized in that the rectifying electrode is made of silver or copper. 6. Process for the manufacture of crystal rectifiers according to Claim 1 to 5, characterized in that as an additive to the metal the rectifying Electrode arsenic or phosphorus is used. 7. Process for the manufacture of crystal rectifiers according to claim 6, characterized in that the amount of additive is a maximum 10 / a. B. A method for manufacturing crystal rectifiers according to claim 6, characterized in that the rectifying electrode made of silver with a There is an addition of 0.1% arsenic. 9. Process for the manufacture of crystal rectifiers according to claims 1 to 8, characterized in that the current-voltage characteristic made visible after electrical formation in a suitable manner, e.g. B. on is imaged on the screen of a cathode ray tube. 10. Use an after the method according to claim 1 to 9 produced rectifier for electrical Tripping circuits. 11. Use of a according to the method according to claim 1 to 9 manufactured rectifier for binary electronic counting devices. Into consideration Drawn pamphlets: Swiss patent specification No. 263 779: Belgian patent specification No. 499,900; British Patent No. 650 007.