DE2363437A1 - METHOD OF OPERATING PHOTO GUIDING VARISTORS - Google Patents

Description

Fr ^ nU -.'-. Vi / iv.Mn 1
Niddastr. 52

December 19, 1973 WK./es./he.

2563-RD-F897

GENERAL ELECTRIC COMPANY

1 River Road Schenectady, N.Y., U.S.A.

Method of operating photoconductive varistors

The invention relates to photoconductors and, more particularly, to embodiments with a photoconductor effect in polycrystalline varistors, which comprise sintered bodies made of a first metal oxide as the main component, and others as an admixture Metal oxides and / or metal halides are added.

A few substances are known, their resistance characteristics is non-linear and is expressed by the following equation

is. . '

Where I is the current flow through the material, ... V is the voltage applied across the material,

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C "'is a constant which is a function of spatial Dimensions of the body, its composition. setting and the parameter of the for the formation of the Body method used is, and

JL is a constant for a given current range and is a measure of the non-linearity of the resistance characteristics of the body.

A well-known example of such varistor materials is Silicon carbide. Silicon carbide and other non-metallic varistor materials are characterized by having a Have exponents alpha less than 6. Recently a Genus of polycrystalline varistor materials with metallic Oxides produced, which has an exponent alpha of more than IO. These new varistor materials include a sintered one Body made of zinc oxide crystal grains and also contain an intermediate grain layer of other metal oxides and / or Meta 11halides, for example beryllium oxide, bismuth oxide, bismuth fluoride or cobalt fluoride and are for example in U.S. Patents 3,682,841 and 3,687,871. Considerable effort has been made on this new varistor material and this gave rise to a number of inventions such as those disclosed in U.S. Patents 2,693,053 and 3,694,626 are described, -However, attempts have been made to generate it a photoconductive polycrystalline metal oxide varistor remained unsuccessful.

The photoconductivity of zinc oxide itself is known. The photoconductivity of pure polycrystalline and monocrystalline Zinc oxide was measured experimentally and reported by Harrison in 93 Phys. Rev. No. 1 on page 52, 1954. Furthermore, is the photoconductivity of zinc oxide and other compounds Group II elements with Group VI elements, for example Research into characteristics and properties and applications

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wise cadmium sulfide, a theoretically predictable phenomenon.

However, the photoconductivity of zinc oxide does not impart any photoconductivity for polycrystalline varistors based on zinc oxide, since the zinc oxide grains have a relatively high conductivity and therefore any change caused by radiation the resistivity of the zinc oxide grains that occur can 'is not observable' because of the high resistance of the. Intermediate material, the oxides and / or halides of others Includes metals. Accordingly, any photoconductivity must be which might be found in such polycrystalline varistors stem from the photoconductivity of the intergrain material. Therefore, despite experimental efforts to achieve this effect, such photoconductivity has not been observed. .

The present invention is related to the concurrently deposited German patent application P to which reference is hereby made.

Previous work with varistor devices made of polycrystalline metal oxide was directed to such devices, which one Have continuity in the bulk of these devices. In the aforementioned German patent application filed at the same time it is described that no photoconductivity can be observed in such devices because of the insufficient Penetration of energy into the facility. It was also found that the photocurrent and the sensitivity of a polycrystalline Metal oxide varistor is a function of the electrical potential that exists across the current-carrying part of the varistor is created. .

One aspect of this invention is a photoconductive polycrystalline Varistor and a method for changing the sensitivity

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ability of the same. This facility is also usable as a photodetector and as a varistor.

According to one embodiment of the invention, a photoconductive polycrystalline metal oxide varistor in the form of a sintered one Pill or disc is provided which has a pair of electrodes arranged on a surface. Between the electrodes a distance is provided which allows electrical currents to pass from one electrode to the other through a part of the varistor material and continue to provide lighting the current-carrying part of the varistor material allows. That Potential applied across the electrodes is selected to provide the desired photoconductor sensitivity and photocurrent amplitude receives.

A better understanding of the invention emerges from the following description of embodiments in connection with the pictures.

Figure 1 is a top plan view of a photoconductive varistor which for carrying out the invention as an embodiment can be used.

Figure 2 is a plan view of a modified form of the photoconductive varistor according to Figure 1, are mounted at the four electrodes on a surface and which is adapted for use in a photo-detector circuit including a circuit for cancellation or Unterdrükküng the dark current.

Figure 3 is a view of a modification of the photoconductive varistor of Figure 1 with coaxially shaped electrodes »

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1 shows a body made of polar crystalline varistor material with a surface on which first and second electrodes II and XP. are arranged. The electrodes It and 12 have substantially parallel opposite edges 13 and 14, which together define a distance 15 between the electrodes 11 and 12 on the surface of the polycrystalline varistor 10.

The varistor 10 is shown in the figure with a circular shape Surface mapped and represents a disk or plate (plinth) made of polycrystalline varistor material. The disk or Platelet shape is easy to manufacture. However, the invention is not limited to this form, and others may as well Shapes, for example a right-angled prism, can be used »

The polycrystalline varistor disk 10 is produced by that a mixture with zinc oxide as the main component and other metal oxides and / or metal halides as secondary components is pressed and is sintered. For a detailed general description for "Preparation of Polycrystalline Varistorseheibeη is referred to the aforementioned US patents 3,682,341 and 3,687,871. In one embodiment of the In the present invention, the varistor disk is made by weight mainly of zinc oxide with bismuth oxide and antimony oxide as secondary components and lesser amounts of other metals. This embodiment shows a varistor slpha exponent from 40 *

The electrodes 11 and 12 are on a surface of a polycrystalline Variator disc 10 applied in a manner known to me and can be applied, for example, as a silver paint or by vapor deposition or cathodic sputtering of such metals as aluminum, Zinc or platinum can be produced. The distance between

82 * 77

parallel opposite edges 13 and 14 of the electrodes is selected so that the varistor voltage the establishment is intended. The varistor voltage is accordingly a function of the width of the gap or gap 15. The Gap 15 also enables the live part of the variator disk to be illuminated .10.

In operation, the application of an electrical potential difference causes between the electrodes 11 and 12 a current flow between the electrodes through the part 15 of the varistor disk 10. The amplitude of this current is given by the following equation:

JJ is a positive function of the intensity and frequency of the electromagnetic energy which illuminates the gap or gap 15 and the electrical potential across the gap 15. The other parameters have already been defined above.

As can be seen from the above equation, the amplitude of the photocurrent generated in a photoconductive polycrystalline varistor is a function of the electrical potential between the electrodes. The photosensitivity of the photoconductive varistor is also a function of the potential versus the distance. The sensitivity is inversely proportional to the potential. This means that at lower voltages the ratio of dark current plus photocurrent to dark current is greater than at higher voltages. -The following table illustrates the relationship between the electrical potential over the distance 15 on the one hand and the amplitude of the photocurrent and the sensitivity of the photoconductor on the other.

Ip amps
(at Konstanter
Lighting
intensity) TABLE I. ν
volt 1,2PxIO " ⁹ I (without Be
lighting)
amp 0.5 1,2FxIO " ⁸ RxtO " ¹² 5 1.25xiO " ⁷ BxlO ^"1 · ¹ FO I, FxIO " ⁷ 2xlO " ⁹ ' 60 3.5x10 " ⁷ 4.3x10 " ⁹ 80 2.7 x 10 " ⁶ 4x10 ~ ^R 100 2.4 x 10 ~ ⁵ l, 2x10 " ⁶ 116 2, OxIO " ⁴ 1, IxIO " ⁵ 120 2. OxIO " ³ 1, OxtO " ⁴ 12R 1. OxIO " ³

ΔΙ (generated by light)

amp

1.24x10 1.24x10

-9

-8th

1.23x10 "'1.5χ10" ⁷

3.1χΐθ ~ ⁷ -6

1.5x10 1.3x10 1.0x10 1.0x10

-4

-3

As the table above shows, the photoconductive varistor is according to the invention extremely sensitive at low operating voltages. For example, in the range from 0.5 to 5 volts, the ratio of the sum of the photocurrent plus dark current to the dark current is of the order of magnitude of 6000. On the other hand, in this low voltage range, the amplitude of the photocurrent is very high small amount. According to the invention is therefore the operation of the photoconductive Varistors at low voltages suitable for such applications as the precision measurement of radiation intensity, for which the highest sensitivity is needed and which is convenient Amplifiers with high gain and low noise can be included in the processing device, which receives the output signal of the photoconductive varistor.

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The TpbeJIe also shows that at high voltages applied Photocurrent with a relatively large amplitude is obtained. on the other hand is then the sensitivity of the photoconductive Varistor greatly reduced. For example, the table shows that at a voltage of 198 volts across distance 15, the ratio the sum of the photocurrent plus dark current to the Durikelstrom 2 is. However, a photo current with a current strength of 1 mA is available and when compared with photo multiplier tubes This value is very favorable in the electricity company and thanks to the new method, this current intensity can also be used significantly lower costs can be achieved. It should be noted here that the data presented in Table I cover the voltage range from 0.5 to 128 volts across the electrode path of a certain photoconductive polycrystalline varistor element include. The data given have been carefully executed and get controlled experiment. The invention is of course not limited to the data in Table I, since other experiments have shown that the data in Table I can be safely extrapolated with sufficient accuracy can. The operation of photoconductive Hp Ibleitervaristorsen is according to the invention at high voltages suitable for applications in which a direct utilization of the output side Photocurrent of a photodetector is desirable, for example for operating a small motor and for automatic shutter adjustment.

As can also be seen from Table I, the high-voltage operation leads of a photoconductive polycrystalline according to the invention Varistors cause relatively large dark currents, which can be very inconvenient in some applications. In such applications, a compensation for the dark current is therefore provided according to the invention intended. At a given operating voltage is the dark current has a constant value and therefore a compensation can be created by introducing a counter value

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an opposite current for the dark current in a bridge circuit is made with a constant current source from a battery and a resistor, another previously known Compensation method, which with the photoconductive varistor according to of the invention can be used, consists in a Zerhnckervorgang on the electrode distance or the distance η to carry out the energy and as a downstream evaluation device such a device with a frequency discriminator effect to use, for example an amplifier circuit with a series capacitor in the input. Alternatively, according to In an embodiment according to FIG. 2, compensation is provided will. In the embodiment according to FIG. 2, the varistor disk has 10 two pairs of, electrodes, which are on a surface the same are arranged. The electrodes 11a and 12a form the photoconductive electrodes and operate as described above with reference to electrodes 11 and 12 of FIG became. The electrodes 11b and 12b are the reference electrodes. That part of the distance distance 15, which the Forms varistor conduction path between electrodes lib and 12b, is covered with a shielding part, not shown, which prevents the radiation from striking this part. Accordingly dark current and photocurrent flows between electrodes 11a and 12a, and flows between electrodes 11b and 12b just a dark current. Because of the door of the varistor material no cross currents flow, for example between electrodes 11b and t2a or 11a and 12b. The between the electrodes lib and 12b current flowing against that between the electrodes tla and 12a are switched to flowing current. this happens in a conventional bridge formwork to avoid the dark current component from the output of the photoconductive varistor to eliminate. This method has the opposite of the method with Counter-connection of a current from a constant current source Advantage of it for a given photoconductive varistor device can be used at any operating voltage without emergency

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willingness to change the components of such a power source for the counter-current. This method owns. the advantage over the previously known chopper method that they a DC output signal with a higher power level supplies for further use.

Figure 3 shows an alternative embodiment of the photoconductive polycrystalline varistor according to the invention, the coaxial has mutually arranged electrodes and a varistor disk to with a circular electrode 12c and an annular electrode Contains electrode lic, which is applied to the disc are and an intermediate annular gap or space 15 define.

The compensation method described in connection with FIG. 2 can also be used with a modification of the electrode arrangement and a corresponding further simplification. In the embodiments according to Figures 1 and 3, a second pair of electrodes is applied in the same pattern on the opposite, invisible surface of the varistor disc 10, Sin such an electrode set, then acts as an electrode pair for the photoconductor and the other electrode set serves as a source for the Reference dark current. In this case, however, the varistor disk 10 itself shields the reference electrodes from the radiation and this eliminates the need for a separate shield as discussed in connection with FIG.

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Claims (1)

Ps tenta nprü. before Method of operating a photoconductive varistor with a first pair of electrodes disposed on one surface of a body of polycrystalline varistor material is, with the electrodes having an interposed distance; characterized in that the method comprises the following steps * an electrical potential is applied between the electrodes, this potential is selected so that it the sensitivity and amplitude of the photocurrent of the photoconductive Varistor determined, the photoconductive varistor is placed in such a position that he has the energy to be recorded or measured records, A current flowing between the electrodes across the electrode spacing is received in an evaluation device, where the current is proportional to the potential and the intensity which is energy. 2. The method according to claim 1, characterized in that to achieve maximum sensitivity, the electrical potential at a low voltage value is selected. 3. The method according to claim 1, characterized that to achieve a large amplitude of the photocurrent, the electrical potential with a high Voltage value is preselected. AO9827 / 1004 A method according to any one of claims 1 to 3, wherein in the absence of those picked up by the photoconductive varistor Energy a dark current flows between the electrodes,. characterized in that the dark current is eliminated by the electric current, which is proportional to the intensity of the energy. 5. The method according to any one of claims 1 to 4, characterized in that the step of removing of the dark current is that the current flowing between the first pair of electrodes is in a bridge circuit is switched against a constant current, which is equal to the dark current. Method according to one of Claims 1 to 4, characterized. that on a surface of the A second pair of electrodes is arranged in the varistor body, this second pair of electrodes having an intermediate Has second distance and this second distance is shielded from the einrrhl th energy, so that between this second pair of electrodes only dark current flows, and this process step of eliminating the dark current the counter circuit of the between the first pair of electrodes flowing current against the dark current flowing between the second pair of electrodes in a bridge circuit contains. . . 7. The method according to any one of claims 1 to 4, characterized characterized in that the process step of Eliminating the dark current causes a chopping process to occur includes sensing energy and this process step U 0 3 B 21I 10 Ü U furthermore the filtering out of a direct current component eus the current contains ^ which is proportional to the intensity of this Energy is. 409827 / 10CU Le e rs e ite