DE4211865A1 - LIGHT-SENSITIVE ELECTRONIC SWITCH FOR HIGH STROEME - Google Patents

Abstract

The switch described uses interdigitated indium and silver electrodes closely spaced on the surface of a photosensitive semiconductor and an intense source of light such as a xenon flashlamp. The semiconductor and electrodes may be arranged on the surface inner of a hollow spherical cavity at the centre of which is the light source. The switch is designed to carry high currents (typically 10A) at relatively low voltages (typically 5kV).

Description

The present invention relates to an electronic switch with egg a photosensitive semiconductor and in particular an electroni Switch according to the preamble of claim 1, which is for high Currents is suitable.

From GB 89 05 910.9-A and GP 90 18 957.2-A are already lichtemp sensitive electronic switches known. These switches will be used as a light source in each case LEDs. The switch in the on second application mentioned is with a Rated voltage greater than 30 kV, and with a current that ge ringer than 0.2 A is operated. These conventional lichtempfindli Chen electronic switch thus have the disadvantage that ever because light source used a relatively low intensity and a relatively long climb time and also the Disadvantage that they are for high currents at relatively low span tions are not suitable.

It is therefore an object of the present invention to provide a lichtemp to create sensitive electronic switch, which has a similar chemi composition as a corresponding conventional switch has, however, in contrast to such a switch a continuum tional current of more than 10 A at a maximum rated voltage can transport from 5 kV and also an intense lighting having a very fast rise time.

This task is used in a photosensitive electronic Switch of the generic type according to the invention solved by the Features in the characterizing part of claim 1.

The switch according to the invention is in contrast to conventional Photosensitive electronic switches as a high-performance switch suitable.  

The light source of the switch according to the invention preferably generates an intense radiation in a narrow band of frequencies, attached to the Characteristic of the photosensitive material is adapted. alternative can be used a light source that has a light radiation with a wide Fre. containing the respective narrow frequency band generated quenzband. The light source is relative to the photosensitive Material according to the invention arranged so that the light generated effek tiver is used.

An important feature of the present invention is the Geometry of the switch electrodes of the photosensitive layer. These Geometry differs significantly from the one mentioned conventional switch and is designed so that the flow of current between maximizes the electrodes and heat dissipation from the light sensitive layer is increased.

The geometry of the electrodes is such that each (e.g. shaped) electrode has a large length in the circumferential direction and that the distance between the two electrodes is small. In the Ver equal to a corresponding conventional electrode geometry, in which two substantially rectangular electrodes on the upper surface of a semiconductor layer in a relatively large against side distance, is in the electrodes according to the invention geometry is the path the current travels from one electrode to another must be reduced, in addition, the available Rung broadened. Both factors work that the cons stood between the electrodes is reduced, so that a high Current flow is possible. Typically, the distance between the Electrodes in the order of 2 mm.

Preferably, the semiconductor forms part of the inside of a Hollow sphere, in the center of which the light source is arranged. A such arrangement maximizes the degree of utilization of light source of emitted light.  

Another preferred feature of the present invention is in the fact that the electrode on the surface of the semiconductor is formed interdigitated. With this arrangement it is achieved that while maintaining relatively small dimensions, the length the electrodes in the circumferential direction can take a large value and the two electrodes angeord at a small mutual distance can be net.

Other objects, features and advantages of the invention are in the Subclaims, referring to preferred embodiments of the above relate to the invention.

The invention will be described below with reference to a preferred embodiment explained in more detail with reference to the drawings; show it:

Fig. Dung 1 is a schematic cross section through a partially fer tiggestelltes electronic device according to an embodiment of the present OF INVENTION be vorzugten;

Fig. 2A, B is a plan view and a cross-section, respectively, of a portion of the device of Fig. 1, each for explaining the electrode arrangement; and

Fig. 3A, B shows a cross section and a plan view of the completely finished electronic device according to the embodiment of FIG. 1.

In all figures and in the following description designate the same reference numerals each have the same parts of the component.

In general, the device shown in the figures comprises a semi-spherical alumina housing 1 , in the interior of which a sintered photosensitive layer 2 is formed, which has a complex Kadmi compound containing the following composition: 58-72% by weight of cadmium, 14, 8-21% by weight of selenium, 7-15% by weight of tellurium, 7-12% by weight of sulfur, 0.1-1% by weight of chlorine and 0.005-0.1% by weight of copper. The alumina hemisphere 1 is in a hemispherical cavity of an aluminum block 5 eingelas sen, which acts as a heat sink. As shown, the illumination source 6 is positioned substantially in the center of the circle defined by the boundary line of the clay earth hemisphere 1 . Above the clay earth hemisphere, a hemispherical reflector 7 is arranged, which completes the alumina hemisphere to a solid sphere cavity and ensures that substantially all of the light source generated by the light source 6 falls on the photosensitive layer 2 . The electrodes 4 a and 4 b are given by interdigitated, concentric rings 4 a 'and 4 b', which are formed on the surface of the lichtempfindli chen layer 2 and separated by a small distance of typically 2 mm.

The device described has a Leitungswi with exposure Resolved less than one ohm and without exposure a lei resistance of more than 15 million ohms. The transport capa For continuous current is more than 10 amps, the Bauele is designed for surge currents for more than 100 amps. The ma maximum rated voltage is 5000 volts, while the maximum Rated power is 100 watts. The specified nominal sizes for the Electricity and power are very conservative estimates of where is to be expected that in further development work by many Magnitudes can be increased.

The preparation of the photoconductive device shown requires the following four basic levels:

Step 1:
Preparing the materials;

Level 2:
Applying the mixed materials to an electrically insulating surface to form a layer;

Level 3:
Sintering the layer to produce a polycrystalline photosensitive layer;

Level 4:
Attach the electrical contacts on the sintered layer.

Now, each of these stages will be described in detail.

Step 1

The materials used in this process must be of the highest quality Purity, d. H. of a purity of 99.999% or more, so that the process can be executed successfully. It is also desirable that the materials in a finely powdered form with a particle size of less than 3 microns are present.

In the particular example considered, the following are mate used:

Cadmium Selenide (Cd.Se)
Cadmium sulphide (Cd.S)
Cadmium chloride (Cd.Cl)
Copper chloride (Cu.Cl)
Tellurium (Te)
Turpineol (CHO) organic solvent
Ethyl cellulose (organic binder)

First, all of the non-organic powders in this be special example in the following weight ratios with each other mixed:

Cadmium selenide | 40.3% Cadmium sulfide 40.7% Cadmium chloride 8.9% Copper chloride 0.1% tellurium 10.0%

The proportions can be used to adjust the electrical properties may be used, but they may be grounded not in addition to the range of compositions given above differ.

First, the powders are mixed and then in a me churned dry, such as a "Microliser" to ensure that they are completely mixed together and no clumping occurs. The examination of the mixed and Ground powder in this stage should show that all Parti kel have a diameter which is smaller than 3 microns.

Level 2

If the mixed powders are prepared, the next step is to be sprayed on the inside of the gezeig th in Fig. 1 electrically insulating alumina ceramic hemisphere 1 convert turn into a suspension of the mixed and milled powder, which is suitable. The hemisphere 1 is typically formed of 96% alumina ceramic and has a diameter of 10 cm and a wall thickness of 0.5 mm.

To prepare the suspension, the powder with a suitable Liquid and a suitable binder mixed so that the Particles are held together when the sprayed layer ge is dried. For this task, the liquid TURPI NEOL and chosen for the binder ETHYL CELLULOSE.

To convert the powder into a suspension suitable for spraying is suitable, the ethyl cellulose is first dissolved in Turpineol, the Weight ratios by 10% by weight and 90% by weight, respectively give. The resulting solution is then mixed with the Pul  ver in ratios of about 25% of the solution and 75% of the Pul mixed to produce a thick, smooth liquid; in this connection the exact conditions can not be specified, since the feast The determination of the correct viscosity of the liquid to a great extent part of the professional concerned. Then the Sus pension finished and can be sprayed on the inside of the hemisphere the.

The deformability of the photosensitive layer which is possible at high electrical voltages can be increased and irregularities of the layer thickness, which could produce uneven electric fields, can be compensated for by applying this layer to a stress relieving layer of a material weakening the electrical stress previously on the surface of the aluminum substrate has been formed is produced. This relaxation layer must be chemically stable up to a temperature of 600 ° C in order to minimize chemical interaction between the stress relief layer and the photosensitive material layer thereon. For example, the layer 3 may be a silicon carbide powder bonded with an electrically insulating glassy glaze, which glaze also binds the powder to the substrate. The electrical properties of this layer are determined by the size of the grains, the density, the thickness and the dimensions of the layer. Typically, the electrical properties for a 15 μm thick layer of the type used in this device are such that at an electric field strength greater than 25 kV / cm, the layer suddenly becomes conductive. This prevents the formation of local areas with high electric fields.

Before spraying the photosensitive layer 2 on the inside of the alumina hemisphere 1 , a suspension composed of silicon carbide powder and the glassy glaze is sprayed on the inside of the hemisphere to a thickness of 25 μm. Then, the stress relief layer 3 is heated to 900 ° C to form a uniform hard glassy layer about 15 μm in thickness containing silicon carbide particles.

Subsequently, the Sus sus pension containing the photosensitive material is sprayed onto the surface of the first relaxation layer to a thickness of about 25 microns. The hemisphere 1 , on which the layer has been sprayed, is then placed in an oven and heated at 100 ° C for 10 minutes to evaporate the solvent (turpineol) leaving behind the ETHYL CELLULOSE containing the particles of the powder connects, so that a uniform layer 2 is formed, which adheres to the relaxation layer 3 .

After this final stage 2 step, the alumina hemisphere 1 and layers 2 and 3 can be handled safely and stored if necessary, this product now ready for sintering.

level 3

The sintering step involves placing hemisphere 1 and layers 2 and 3 in a closed Pyrex glass container (Pyrex is a trademark) into which low flow rate nitrogen is introduced, to which a small, controlled percentage of oxygen in the form of air is added. Typical flow rates are between 4 and 6 liters per hour with the nitrogen and other gases released from the sintered layer being vented through a small bore in the lid of the container. It has been found that the pyrex glass is the most suitable mate rial for the container. Other materials such as stainless steel or molten silica are attacked by the gases exuding from the layers and therefore are not suitable.

For sintering the layers of the photosensitive material, a special, electrically heated tube furnace can be used. It can  However, most types of electric ovens respond accordingly provided they provide uniform heating mung of the substrates.

The sprayed onto the inside of the hemisphere 3 layer 2 is placed in the Pyrex glass container, then the lid is brought into Posi fled, the lid is not adapted to be gas-tight, to allow the free passage of nitrogen through the container. Then, gas is passed through a Pyrex glass tube into one end of the container, which flows through the container and exits again at the opposite end. Prior to heating, pure nitrogen is passed into the tank for a period of 20 minutes to empty the initial air. Then the oven and the container are brought to a temperature of 520 ° C for 50 minutes, during which time pure nitrogen is passed through the container to ensure that no air enters the container. Once the container has been brought to the required temperature, a controlled percentage of air is added to pure nitrogen to allow controlled oxygen absorption in layer 2 during the sintering process. In the composition described above, the ratio of nitrogen to air 97: 3, wherein the total flow of Gasge mixed is limited to 4.5 liters per hour. Subsequently, the oven temperature is maintained at 520 ° C for 10 minutes, during which time the gas flow is maintained. After the lapse of these 10 minutes, the oven is switched off so that it can cool for a period of between 60 and 90 minutes, wherein air can be blown into the oven to accelerate the cooling. The flow of the nitrogen / air mixture is kept on Maintain until the temperature has dropped below 150 ° C.

The mixture of air and oxygen has a strong influence on the conductivity with and without exposure of the layer 2 during the sintering process. If too much oxygen can enter the photosensitive layer 2 , photosensitivity is lost, but this property can be restored if the material is reheated in vacuo.

The sintered layer produced by the above-described heat treatment is solid, adhesive and chemically stable. During the sintering stage there is an approximately 40% reduction in the thickness of the layer 2 . Electron microscopic studies of the surface show that the sintered layer consists of large grains of about 9 microns, which are fused together at their edges.

The analysis of layer 2 shows that the final compositions are similar to those known from the above-mentioned GB 90 18 957.2-A.

The composition ranges are indicated below. Under the generic term "process", the compositions of the mixture are stated at the beginning, while under the generic term "product" the mixtures of the finished layer 2 are listed:

Process CdSe | 32-47% CdS 32-47% CdCl 4.7 to 13% CuCl 0.01-0.1% Te 7-15%

product Cd | 58-72% se 14.8 to 21% S 7-12% Cl 0.1-1% Cu 0.005-0.1% Te 7-15%

In Fig. 1, the cross section through the hemispherical housing 1 is shown in this stage, wherein the photosensitive layer 2 and a preferred feature of the present invention representing Ent voltage layer 3 are shown.

Level 4

After removal of the hemispherical housing 1 and the light-sensitive layer 2 from the oven, the electrodes 4 a and 4 b attached to the surface of the photosensitive layer who the. The geometry of the electrodes is such that the length of Elek electrodes in the circumferential direction receives a maximum value, whereby the line resistance is reduced upon exposure of the switch and the current carrying capacity can be increased. In the present embodiment, this geometry is achieved by forming the contacts as a group of interdigitated, narrow concentric fingers 4 a 'and 4 b' separated by a gap of typically 2 mm (for operation at 5,000 volts) as shown in Fig. 2. The fingers 4 a 'represent the part of the electrode 4 a, while the fingers 4 b' represent the part of the electrode 4 b.

To apply the electrodes on the photosensitive layer, on the surface of the photosensitive layer 2, a Metalli cal, arranged hemispherical mask having slots of 1 mm, which are cut out in a shape that the formation of the above-mentioned group of interdigital contacts allowed. First, indium is vapor-deposited through the slits of the hemispherical mask, which is a sieve for the surface of the layer, to a thickness of 0.1 μm. Subsequently, by the same mask on the In dium silver evaporated to a thickness of 0.5 microns to improve the elec tric conductivity of the interdigital contacts. At closing, the mask is carefully removed from the photosensitive layer 2 . After this operation, the alumina hemisphere 1 , on which the photosensitive layer 2 and the electrodes have been deposited, placed in an oven and heated to 160 ° C for 5 minutes, to melt the indium into the Oberflä surface of the layer 2 to enable. This process must be performed carefully to ensure that in the surface only the In and not the silver diffuser diffused, since the latter could affect the egg characteristics of the photosensitive material 2 .

The photosensitive layer produced by this process and the mentioned special geometry of the contacts produce a line resistance without exposure between the electrodes 4 a and 4 b of at least 5 million ohms in complete darkness and a line resistance of 250 ohms at a 2500 lux exposure of one tungsten lamp.

Mounting the switch

Because this switch type is intended for use at high currents is hen, it is desirable that the line resistance with Belich for this use is less than 1 ohm. This is in the present embodiment as an exposure source, a xenon flash used light.

The term "flash" refers to a light source type that opti emits radiation when excited by the excitation with an electric a gas is ionized in the field.

Such lamps are often used for pump lasers. It is usual, this lamp type by the discharge of a capacitor over two To supply power to the electrodes of the lamp and the emitted to quantify optical radiation by their energy (Joules).  

In the present invention, flash discharge tubes such as a xenon lamp is preferred since it is an economical means of er production of intense light. They are photoelectric efficiencies of 60% possible, with the rise time few Microseconds, and can also be used for high performance types Several 100 joules are emitted for several milliseconds. The Broadband emission of a xenon flash tube is for many types of light sensitive conductors and includes a wavelength range from 200 nm to more than 1000 nm of the electromagnetic spectrum. Therefore, in the present invention, the use enables the This exposure source type is an exposure of the photosensitive Ma terials with a very high exposure, so that a ratio Moderately high conductivity of the photosensitive material hervorgeru can be fen. The disadvantage of a flash tube, however, is that all types have a limited life, so that the Number of switching operations that the switch can perform on ei 100 million is limited. Therefore, the flash tube is intended in future embodiments of the present invention to replace light emitting diodes.

The tube type selected for the present embodiment is one pulsed xenon lamp with short arc, which at a rate of 50 flashes per second with each flash 0.75 J of optical energy can witness.

The alumina hemisphere 1 with the photosensitive coating 2 is in the hemispherical cavity of a block 5 made of metal, for. As aluminum or copper, which acts as a heat sink, arranged. First, on the outside of the alumina hemisphere 1, a coating of a thermally conductive lubricant brushed to rule between the alumina hemisphere 1 and the inner surface of the hollow space to ensure a good thermal contact. The interior of the hemisphere can be filled with an electrically insulating liquid such as liquid fluorocarbon, on the one hand to prevent flashover between the electrodes 4 a and 4 b and on the other hand to improve the heat distribution. The xenon flash tube 6 described above is then positioned so that the short arc in the tube is located substantially in the center of the circular boundary line of the hemisphere. Subsequently, a cover, which is gege ben by a hemispherical reflector 7 , placed over the alumina hemisphere. In Fig. 3, the fully constantly completed device according to the present Ausfüh tion form is shown, in which the light source 6 and the lichtemp-sensitive material 2 are inside a hollow, substantially spherical space.

Optical properties

The maximum optical response is about 680 nm, with response at 830nm 10% and 560 nm is 20% of the maximum sensitivity, so that a wide band is available, which is about the volume through the xenon flash tube generated exposure corresponds.

Electrical Properties dark conditions

At a DC voltage of 5000 volts, which is connected to the contacts of the light sensitive layer is applied, a current of less than 240 uA to be expected, so that a line resistance without exposure of the switch, which is more than 16 megohms.

The electrical breakdown of the photosensitive material occurs 5500 to 6000 volts of a DC voltage, as can be seen from tests ben, who participated in several test copies with similar contact columns were executed.  

exposure source

As the exposure source, a xenon flash tube is used which has a optical radiation in the range between 200 nm and 1000 nm of electromagnetic spectrum at a rate up to 50 flashes per Second and with an energy of 0.75 J per flash and a duration emitted by 10 ms.

Test regarding the time response behavior

When a direct current is applied to the contacts of the photosensitive layer Bias voltage of 10 volts, generates the xenon flash tube, which meets the above-mentioned specifications, in this 10 volt before voltage circuit current pulses.

The characteristics of these pulses are the following:

Peak current: 17.5 amp;
Time between minimum current and maximum current, the time zero indicating the beginning of the flash: 4.7 μs;
Duration during which the current drops to 1% of the peak value, calculated from the end of the flash of light: 9.7 μs;
estimated minimum resistance: 0.57 ohms.

Advantages over other electronic switch components:

• 1. The rated current of the switch is much larger than other types of semiconductor switching elements.
• 2. Unlike other high-power semiconductor switches can the voltage drop across the device in the conducting state be lowered to less than 1 volt.  
• 3. The driver circuit is complete of the switch device electrically isolated.

Claims (11)

An electronic switch comprising a photosensitive semiconductor ( 2 ), two electrodes ( 4 a, 4 b) arranged on its surface and a light source ( 6 ) which in the active state clears the semiconductor ( 2 ) and causes it to between the two electrodes ( 4 a, 4 b) to produce an electrically conductive path, characterized in that
the photosensitive semiconductor ( 2 ) is a sintered mixture containing 58-72% by weight cadmium, 14.8-21% by weight selenium, 7-15% by weight tellurium, 7-12% by weight sulfur, 0.1% 1% by weight of chlorine and 0.005-0.1% by weight of copper, and
the geometry of the electrodes ( 4 a, 4 b) on the semiconductor ( 2 ) is such that the dimension of each electrode ( 4 a, 4 b) in the longitudinal direction has a large value and that each electrode ( 4 a, 4 b) is located at a short distance from the other electrode. 2. Switch according to claim 1, characterized in that the electrodes ( 4 a ', 4 b',) are interdigitated on the surface of the semiconductor ( 2 ). 3. Switch according to claim 1 or 2, characterized in that the electrodes ( 4 a, 4 b) comprise indium and silver. 4. A switch according to claim 1, 2 or 3, characterized in that the semiconductor has the form of a layer ( 2 ) which adheres to an electrically insulating substrate ( 1 ). 5. A switch according to claim 4, characterized in that between the electrically insulating substrate ( 1 ) and the sintered semiconductor layer ( 2 ) an expansion layer ( 3 ) is provided which adheres to the substrate ( 1 ) and a molten mixture of a finely divided, non-linear Resistance material and an electrically iso-insulating glassy glaze comprises. 6. Switch according to claim 5, characterized in that the nonlinear resistor material is silicon carbide. 7. Switch according to claim 4, 5 or 6, characterized in that the semiconductor layer ( 2 ), the substrate ( 1 ) and, if present, the relaxation layer ( 3 ), form a hollow hemisphere. 8. A switch according to claim 7, characterized in that the light source ( 6 ) is arranged substantially in the center of the circular limita tion line of the hemisphere ( 1 , 2 , 3 ). 9. A switch according to claim 7 or 8, characterized by a hollow, hemispherical, reflective cover ( 7 ), which forms in connection with the hollow hemisphere ( 1 , 2 , 3 ) a hollow, spherical space. 10. Switch according to one of the preceding claims, characterized in that the light source ( 6 ) generates an intense electromagnetic radiation with a frequency responsive to the lichtemp sensitive semiconductor ( 2 ). 11. A switch according to claim 10, characterized in that the light source ( 6 ) is a xenon flash lamp.