DE1097568B - Process for the production of a semiconductor device with a uniformly sintered body made of alkaline earth titanates - Google Patents

Description

GERMAN

The invention relates to the production of a semiconductor device, ζ. Β. a rectifier or a Capacitor with a semiconductor material or a barrier layer as a dielectric, with a uniform Body made of a material with a high dielectric constant and the properties of a semiconductor, on which conductive electrodes are attached.

Such arrangements can be used as rectifiers, thermistors, varistors, capacitors or in Find the form of their combinations.

A semiconductor switching diode which is used for storing information is already known. In this known diode, a semiconductor body with an n- and a p-conductive zone is a Ferroelectric attached. The conductivity of the surface area is determined by creating an inversion layer changed, so that this also changed the conductivity between two connection points will. Furthermore, a semiconductor body with two zones of p-conducting and η-conducting material is included an intermediate, rectifying layer transition known. On this semiconductor body is applied a ferroelectric layer which is covered by an electrode. By polarizing the polarizable, electrically conductive ferroelectric is the conductivity via the associated electric field the parts of the semiconductor body immediately below it.

Furthermore, a semiconductor arrangement with a non-linear characteristic is already known, which consists of semiconducting Material of high dielectric constant is made. This either has a relatively thick, effective one Barrier layer or a relatively large, pointed electrode.

It is also known to produce an insulating body made from a mixture of very high dielectric constant To produce barium titanate and strontium titanate and oxides of the rare earths by pressing them Mixture placed on a carbon block in a gas-heated furnace and there in an oxidizing Atmosphere with an excess of oxygen a temperature of about 1360 ° C is fired. The materials produced in this way have a very high dielectric constant of about 20,000, a power factor of less than 13% and a resistance of more than 20 MOhm. These substances own no semiconductor properties.

The aim of the method according to the invention is to create a semiconductor device with a contact between a semiconductor body and a conductive electrode, which has the electrical properties this arrangement specifies. Such an arrangement should be particularly compact and can be used as a rectifier or as a capacitor with high capacitance values, a method of manufacture

a semiconductor device with a

evenly sintered body

from alkaline earth titanates

Applicant:

Globe-Union Inc.,

Milwaukee, Wis. (V. St. A.)

Representative: Dr.-Ing. K. Boehmert

and Dipl.-Ing. A. Boehmert, patent attorneys,

Bremen 1, Feldstr. 24

Rolland R. Roup and Jack St. Clair Kilby,

Milwaukee, Wis. (V. St. A.),
have been named as inventors

serve whose electrical losses are sufficiently small.

This object of the invention is achieved in that the sintered body by all-round reduction in a reducing atmosphere to an η-conductive semiconductor body with a Dielectric constant of about 6000 is converted that on this semiconductor body two electrodes made of silver, platinum, zinc or graphite are applied so that between at least one electrode and an insulating boundary layer approximately 0.0025 mm thick is formed on the semiconductor body. This barrier layer has the same chemical properties as the semiconductor itself. It is believed that this layer is caused by positive charges in the semiconductor and immobile negative charges is formed on the inner surface of the conductive electrode, which cause this layer as Isolator works. The thickness of such a barrier layer is determined primarily by the dielectric constant of the semiconductor material and the number of excess carrier ions in the semiconductor material is determined. This thickness is extremely small. The capacitance at a single junction increases to the square root of the dielectric constant and is not directly proportional to this, as is otherwise is generally the case. It is therefore considered appropriate to use a high dielectric constant

009 699/398

3 4

as well as for a small number of excess, a diagram that shows the cross-sectional free charge carriers, in order to prevent the view from being aligned and the charge distribution The barrier layer becomes so thin that it is supercrystalline due to the raw poly- and relative thickness of the barrier layer Surfaces is covered. gang represents

The uniform 5 Fig. 10 produced in accordance with the invention is an enlarged side view of a Semiconductor arrangement consists of sintered metal-usual capacitor with two electrodes passing through oxides with high dielectric constant. In this case, an insulating material is separated from one another, and The materials and firing methods used result in a slide below, aligned with this representation η-conductive semiconductor, in which the number of grams of charge distribution and relative potencies Electrons are limited in number. io tial separation in such a capacitor,

The electrode can be applied to the semiconductor by means of FIG. 11 a diagram of the curve of the direct current edge Metallization process, for example by transverse resistance at different temperatures of the burning of silver or platinum, vapor deposition of semiconductor arrangements according to FIGS. 1 and 2, with on Zinc, by applying graphite resistance paint, the temperature in degrees Celsius and on the abscissa and by other known methods applied 15 of the ordinate the percent resistance at a will. Temperature of 25 ° C is shown,

The extremely thin barrier layer (insulation layer), Fig. 12 a diagram, vertically in logarithmic order, which lies below the conductive electrode, is essential scale that the direct current discharge at different for the capacitance of the semiconductor arrangement, these NEN applied voltages of such an arrangement can therefore easily by enlarging the surface 20, with the applied voltage being increased on the abscissa. A waffle-like pattern or in volts and on the ordinate in the reverse direction a flowing current consisting of depressions and elevations is plotted in microamps,
Surface increases the capacitance of the semiconductor Fig. 13 is a diagram in which the temperature arrangement is greatly increased without the diameter of the coefficient of capacitance and the curve of the power switching element having to be increased. It is not 25 factor of such an element are given, whereby it is necessary that the electrodes are placed on opposite on the abscissa the temperature in degrees Celsius, on the side of the semiconductor, since the part of the ordinate on the left shows the percentage capacitance of the semiconductor body between these and the barrier 25 ° C and on the ordinate on the right the power factor layers serves as a conductor. is given in percent,

If the semiconductor device as a capacitor 30 Fig. 14 is a diagram showing the DC voltage use should find, then form the junction coefficient shows, as well as a curve of the most powerful under two conductive electrodes on the same factor of such an element at different shaped semiconductor body two through the semiconductor voltages, with the applied on the abscissa capacities connected in series. Therefore the voltage is in volts and on the ordinate is the percent total capacity smaller than with only one blocking value of the DC voltage coefficient from layer would be. However, one can value one of the barrier layers at a voltage of zero and on the right short-circuit by showing the conductivity in the ordinate and the power factor in percent Enlarged barrier layer. This can be borne on.

achieve different ways, for example by, to explain the method according to the invention that the electrode is abraded, or by the fact that the production of a semiconductor device with the conductive electrode with a low-melting high barrier layer capacitance is described. Such solder is coated. This affects the over- serving as a capacitor semiconductor arrangement at the barrier layer or the contact in a standing out of a disk 10 of about 6.35 mm in diameter, which is not yet known, and destroys knife and a thickness of about 0, 64 mm with its insulating effect. As a result, the capacity 45 silver-plated areas 12 is approximately doubled. Such a semiconductor arrangement bonds are connected to the silver-plated surfaces through must be operated in such a way that the soldering agent desoldering or cementing is connected. The disc holding side positive, lowest loss to 10 was obtained from a mixture with the following beers. If one of these barrier layers is removed, the following components are produced:
results in a rectifier. In the figures, 50 barium titanate 84 shows 5%

1 shows a side view of a strontium titanate according to the ver 15%

drive according to the invention manufactured semiconductors _{A mixture of} oxides'

arrangement ^ of rare earth metals 0.5%

Fig. 2 is a sectional view of FIG. 1 along the

Line 2-2, 55 This mixture was formed into a disk

3 shows a side view of a further semiconductor and in air at a temperature of about 1343 ° C

arrangement, made according to the procedure after being ^{fired for about 1} hour. The disc 10 is there-

Invention, after not a semiconductor, but has the properties

4 shows a sectional view of FIG. 3 along that of an insulating material and can be used as a dielectric 4-4, 6ö can be turned. The disc will then be at about

Fig. 5 is a side view of another arrangement, 1176 ° C in a hydrogen atmosphere for about

6 is a sectional view taken along line 6-6 from V2 to 1 hour. The reduction in the

Fig. 5, ■ a hydrogen atmosphere, the disk 10 contains half

Fig. 7 is a side view of a further arrangement, conductive properties. This reduction and the burning

Fig. 8 is a side view taken along line 8-8 of 65 "determine the number of excess

Fig. 7, free electrons appearing in the body. It he-

9 shows a greatly enlarged cross-section, there is an η-conducting semiconductor with only a few

view of the connecting line between the metal excess charge carriers. The disc is

and the semiconductor body according to the invention through to 'a uniform semiconductor with a

According to the method produced arrangement and 70 dielectric constant of about 6000.

After the disk 10 has been reduced, its surfaces are known to produce the electrodes 12 Way smeared with a silver paint, and the disc is again either in air or in Burned nitrogen at around 732 ° C.

In the lower part of FIG. 9, the distribution of the positive and negative charges on one of the barrier layers between the semiconductor material 10 and one of the metal electrodes 12 is shown schematically. The negative charges are on the surface of the metal 12. An equal number of positive charges are distributed over a narrow area near the surface of the semiconductor, as shown in the diagram, and are bound to the negative charges. They form an extremely thin, insulating layer. The thickness of this barrier, represented by T , is on the order of 0.0025 mm. The distribution of the charges in an ordinary capacitor and in a dielectric 24 with two metal electrodes 26 applied thereon is shown schematically in FIG. 10 at the bottom. The positive and negative charges are separated from one another by the thickness of the dielectric 24, while in the junction capacitance the charges are separated from one another by a very thin layer. However, since there are two such barrier layers, the two capacitances thus formed are connected to one another by the semiconducting material. The total capacity is therefore generally about half the capacity of a single barrier layer. Each of these barrier layers also acts as a rectifier. The layers can also be viewed as a capacitance with a resistor connected in parallel. The effective thickness T of each barrier layer is a function of the dielectric constant and the number of excess charge carriers in the semiconductor 10. Therefore, the dielectric constant should be as large as possible so that the barrier layer does not become so thin that it is obscured by the raw polycrystalline surface of the semiconductor body will. The capacitance of this semiconductor device increases with the square root of the dielectric constant instead of being directly proportional to it, as is otherwise the case with capacitors.

In order to determine the properties of a semiconductor arrangement according to FIGS. 1 and 2, leads are attached to the electrodes 12. To determine the curve of the DC leakage resistance of FIG. 11, 4.4 volts DC voltage is applied. For the curve of the transverse current, which is plotted against the applied voltage, according to FIG. 12, the resistance is 10 megohms at 2.5 volts, 1 megohm at 4.25 volts, 0.1 megohms at 5.75 volts. To determine the values for the diagrams in FIGS. 13 and 14, a normal bridge circuit is operated at 1 kHz. In the diagrams of FIGS. 13 and 14, the upper curve represents the capacitance curve and the lower curve represents the power factor. These diagrams show that the capacitor of FIGS. 1 and 2 consisting of reduced titanate has good properties in circuits with up to 4 volts having. With a surface area of 6.452 cm ² , capacitance values between 0.25 microfarads and 10 microfarads are achieved.

The semiconductor 10 containing barium titanate and strontium titanate belongs to the oxide semiconductors. This also includes MnO, Fe ₂ O ₃ , NiO, Cu ₅ O, TiO ₂ and oxides of somewhat more complex structure such as ZnFe ₂ O ₄ , LaMnO ₃ and SrTiO ₃ . The materials used herein contain barium titanate alone or modified with the addition of other materials including alkaline earth titanates, zirconates and stannates. It is believed that the addition of rare earth oxides gives an η-conductive valence semiconductor. If no rare earths are added and the reduction takes place at a higher temperature, for example at around 1343 ° C., then sufficient oxygen is removed from the crystal lattice and a suitable semiconductor is thus formed. When oxidizing (when burning in air) a temperature range between about 1232 and 1371 ° C is useful. When reducing (burning in hydrogen) a temperature range between 1149 and 1232 ° C is favorable if a supplement of rare earths is used.

For the metal electrodes 12, burned-on silver, burned-on platinum or vapor-deposited zinc be used. The small differences between the different methods of applying the Metal on the semiconductor, evidently result from a reoxidation of the semiconductor material which is going on during the burning of the metal. This difference can lead to some Extent can be compensated by the fact that the previous reduction step of the semiconductor accordingly is controlled. So for good results there is a specific method of metallizing the External surfaces not required.

In the first modified embodiment of the switching element according to FIGS. 3 and 4, a layer 14 of a low-melting point (at 124 ° C.) solder is applied to one of the silver electrodes 12. This Solder seems to be the properties of the layer transition between the electrode 12 and the semiconductor 10 to such an extent that the barrier layer below the electrode is short-circuited will. Therefore, the capacity of the semiconductor device is doubled, thereby simultaneously increasing the properties of a rectifier. For this reason, the solder-covered side 14 must be positive be opposite to the other if the arrangement is to be used as a capacitor to avoid losses stay low. This semiconductor arrangement can therefore be used both as a rectifier and as a capacitor be used.

The semiconductor arrangement according to FIGS. 5 and 6 consists of a semiconductor body 16, which with a Series of depressions 18 has been provided on the surface. Otherwise, this semiconductor is 16 the same as the semiconductor 10. Under the silver electrodes 20, a barrier layer becomes essential with larger surface than that of the arrangements of FIGS. 1 and 2 formed with the same external dimensions. Apart from such a waffle pattern, every other pattern is with elevations and depressions useful. Since the barrier layer is quite thin, the capacitance is due to the surface of the disc determined if the elevations and depressions are at least several times as thick as the thickness of the Barrier. The waffle pattern need not be attached to both sides of the semiconductor 16 will. Semiconductor devices that have this waffle pattern on only one side have one Barrier capacitance of 0.4 microfarads versus 0.25 microfarads for the same diameter and flatter Surface.

7 and 8, a further semiconductor body 10 is shown, on one surface of which a pair of Metal electrodes 22 are attached with a small distance from each other in the known manner. There

the total capacitance is determined by the thin barrier layer under each metal electrode, it is not necessary to attach the electrodes on opposite sides of the semiconductor 10. Arrangements, whose electrodes are on the same surface, "θ therefore also have the same capacitance, regardless of whether these electrodes lie on opposite surfaces or on the same side of the semiconductor. Lie however, the electrodes are in the same plane, then there is an increase in the resistance of the conductive one Part of the semiconductor material that connects the two layers because of the greater length this route. Therefore, the power factor in a semiconductor device, the electrodes in one plane lie, higher.

With the exception of the semiconductor arrangements according to FIGS. 3 and 4, those described so far are as labeled symmetrically. These have two opposite, rectifying transitions on the Semiconductor body and therefore show the same characteristic curve for the current in both directions. Does anyone have of these contacts rectifying properties and the other non-rectifying, the arrangement can (like those of Figs. 3 and 4) serve as a rectifier. Hence, such arrangements are said to be asymmetrical designated. As can be seen from Fig. 12, the leakage current is largely dependent on the applied voltage. Semiconductor arrangements with such properties can therefore be used as varistors. Using of a semiconductor with a large temperature coefficient the dielectric constant shows the semiconductor device properties that their Enable use as a thermistor. The semiconductor arrangements can be disk-shaped or also be made rectangular, with or without multiple layers and with or without multiple layers Discs. They could also be tubular with inner and outer electrodes.

Claims (9)

Patent claims: 1. A method for manufacturing a semiconductor device with a uniformly sintered Body made from alkaline earth titanates, e.g. B. rectifier or capacitor, characterized in that the sintered bodies by all-round reduction in a reducing atmosphere to an n-type Semiconductor body with a dielectric constant of about 6000 is converted that on Two electrodes made of silver, platinum, zinc or graphite are applied to this semiconductor body that between at least one electrode and the semiconductor body an insulating boundary layer of about 0.0025 mm thickness arises. 2. The method according to claim 1, characterized in that the body consists of a mixture of Titanates of barium, strontium and calcium and the zirconates of barium and magnesium as well from traces of a mixture of rare earth oxides that barium titanate is formed it is predominantly chosen that this body is then placed in air at a temperature between 1232 and 1371 ° C and then to the uniform reduction of the whole body in hydrogen at a temperature between 1149 and about 1238 ° C for a period of one-half to one Hour is burned and that then silver electrodes by means of metal paint on the surfaces of this Applied to the body and burned to electrodes at a temperature not exceeding 871 ° C, that a thin barrier layer with insulating properties is formed under the electrodes without that the chemical composition of the reduced body changes. 3. The method according to claim 1 or 2, characterized in that the material of the sintered Body is only partially reduced. 4. The method according to claim 2, characterized in that the addition of the rare earths is not greater than 10% is chosen. 5. The method according to claim 2, characterized in that the body still other alkaline earth titanates can be added. 6. The method according to claim 1 to 5, characterized in that stannates are added to the body will/ 7. The method according to claim 1 to 6, characterized in that the body is calcium zirconate is added. 8. The method according to claim 1 to 7, characterized in that a layer of low melting point Solder is applied to one of the electrodes to short circuit the barrier layer. 9. Electrical switching element according to claim 3 to 8, characterized in that at least one Surface of the body is provided with depressions and that at least one of the electrodes is on attached to this indented surface. Considered publications:
German patent application S 530 VIIIc / 21g made known on February 22nd, 1951); U.S. Patent Nos. 2,520,376, 2,791,758, 791 759. 1 sheet of drawings © 009 699/398 1.61