DE1415661A1 - semiconductor - Google Patents

Description

The Carborundum Company 4 »8.1961

niagara tfalls, i.Y./USA

semiconductor

The invention relates to electrical resistance bodies, especially on thermistors, with a single ICr is tall made of silicon carbide.

Among thermistors should be the following electrical Jider stand bodies are understood to be the opposite Temperature changes in a wide temperature range are highly sensitive, i.e. the electrical resistance of the body changes more sensitively with changes the temperature. Thermistors, their resistance decreases as the temperature rises, have a so-called negative ■ temperature resistance coefficient.

Thermistors are widely used in devices for temperature measurement, as well as temperature control, for example for the replacement of thermo-electric elements, especially for medium temperatures up to to about 315 C. Here, the thermistors have various advantages over thermo-electric elements, because they are more sensitive to temperature changes than the latter. Furthermore result thermo-electric Elements of relatively weak indications that need to be amplified in order to operate the circuits. Thermistors, on the other hand, actuate the relays directly, which keeps the costs of the control units low. Thermistors are also used to compensate for changes in ambient temperature for accuracy

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of the electrical measuring device over a large area in hook to maintain the ambient temperature. Farther Thermistors can also be used for time delays.

The invention aims to improve thermistors in such a way that the thermistors are made from a single crystal of pure silicon carbide, or from a specially selected silicon carbide, an element of group III A and W VA of the periodic table being present throughout the body . The electrical connection lines are connected to isolated points on the crystal, exclusively by high-temperature fusion.

The invention is explained with reference to the drawings.

Fig.l shows diagrammatically a thermistor according to the Invention,

Fig »2 shows a top view of a device with a Thermistor according to iug.l.

According to the invention, a certain silicon carbide is in Arranged in the form of a single crystal between at least two electrical lines and stands with them • Lines in contact. The parts are then, for example, spring tensioned on the electrical lines brought into a certain mutual position and then heated so far that the electrical lines with merge the contact points of the crystal. The merging expediently takes place in a protective atmosphere, such as argon, helium, hydrogen, or in a vacuum to prevent the electrical wiring and silicon carbide from oxidizing »

809802/0501

1418661

The YersclunelZBn can be done in two different ways. With a "kind" the electrical lines heated by their own resistance - by one electric current passes through it and so on the melting temperature "brings" until the melting and the connection are established. It can also, the electrical current through one of the electrical lines j. then.through the crystal, and then back to the other electrical line. .

the second type is inserted the whole device into a furnace g, and brought to Yers climelzungs temperature.

According to the drawings, the shenuistor consists of a single crystal IC made of silicon carbide, which is located between two electrical lines 11. The ropes are held in a certain mutual position to one another and are heated in a given way to the temperature of the temperature in order to connect the electrical lines with isolated points of the crystal V ¹ Ig. 1 can be seen, then a Kügelcl: s 12 dvs of ceramic or porcelain Laterial on each side of crystal 10 mounted in such a manner that this, i-.ügelchen environmentally electric wires {

wraps. Las Lü ^ elclieii then runs out and holds the parts in a certain mutual position and reinforces the whole device. ... .

• Jeraäss Fig. 2 is the crystal 10 made of oiliziurakarbid between zv / egg isolated electrics. Lines 11

lZen that on. each side, of the crystal of lien 12 of a kerariischeii cement held in place. The land 13 of the electricity lines are the Exposed to atmosphere, the other ends of the electrical X-eitun ^ ün lead into a, partly ext igen porcelain isolator 14, c.er a Jeil of a. "iitorsucliuri ^ s erätes

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of which the thermistor itself is a part.

IF ^{1 For} the invention, the following five types of silicon carbide crystals come into play:

l) Pure silicon carbide, which is theoretically pure Silicon carbide should be understood. This material is very resistant and has a very high ^ sensitivity to temperature changes. Of the , B value is 27600 ° K.

The B value is the measurement of resistance sensitivity of the body against temperature changes in a certain temperature range, it is calculated from the formula

2 «, 303 10g E ₁

B =

¹ I -4

where R _{1 is} the resistance in ohms at a temperature T _{1, and R 2 is} the resistance in ohms at a temperature Tp, where T and Tp are degrees of temperature in Kelvin.

2) Compensated silicon carbide. This is understood to mean a silicon carbide with P and ff impurities in certain amounts, in trace amounts of only a few parts per million. Compensated Silicon carbide has a resistance of about 100 ohm = cm up to 10 ohm = cm at room temperature, depending on how the material in question is compensated. For example, commercially available colorless silicon carbide is a compensated material and has a B value of about 2000 ° K. Colorless crystals are obtained by choosing commercially available green crystals raw silicon carbide »

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3) Material of Iype P. This silicon carbide has a result positive charge carrier an electrically conductive -, '' speed. The positive charge carriers result from the absence of electrons (holes). A semiconductor the P-Type contains a small but very effective amount of trivalent impurity, such as elements of Group IIIA- of the periodic table. The movement of the positive electrical charge carriers creates an impurity semi-conductor. For this include boron, aluminum and g-allium in trace amounts.

■

Commercially available black silicon carbide contains P-type crystals that are usually found at room temperature have an electrical resistance of about 0.1 to 1 ohm = cm, depending on the concentration of the impurity.

P-type silicon carbide crystals with an impurity level, the .a resistance of about IQ 0hm = cm results are for '.thermistors with high wattage very useful. With the materials of the P-Type the aluminum and boron B values of about 2500 K.

4) M-Type material. This material is a silicon carbide, in which the movement of the negative charge carriers results in electrical conductivity. The resistance is small, namely between about 0.01 to 0.1 0hiu = em. The sensitivity to temperature changes is low. The commercially available green silicon carbide contains I-type crystals, and the presence traces of nitrogen influence the properties of the Η-type, so that the iötnrlert is around 1250 ° K.

Traces of phosphorus and arsenic also affect the ■ material of the B-type. The materials used by the E-types contain nitrogen, phosphorus and arsenic, the elements of group VA. are.

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I ¹ Ur very low temperature display] !, roughly in the range of the temperature of liquid oxygen, silicon carbide of the B'-type can be used for thermistors. In the temperature range mentioned, the low resistance and the sensitivity at low temperatures are advantageous. The silicon carbide of the P-type and the N-type have the lowest resistance of the five materials treated, and the resistance depends on the concentration of the impurities. But the same proportions of impurities are found in silicon carbide

»As a P-Type result in a greater resistance / with the Silicon carbide of the Η-type. sensitivity with regard to the \ 7ider stood at the P-type larger than the H-type.

5) Boron in solid solution with silicon carbide. This material differs from P-type silicon carbide. The P-type silicon carbide containing boron has little resistance. The boron content is below 0.015έ. But boron in solid solution in silicon carbide, if the boron content is above 15ε, the result is a higher one Resistance due to the destruction of the silicon carbide grid s.

The crystals of silicon carbide with boron in solid Solution are different from the ordinary silicon carbide crystals. The crystals have a fishscale-like shape Appearance, while the silicon carbide crystals have hexagonal crystal faces. During the X-ray examination of silicon carbide crystals with boron in • solid solution, the lines of expansion are layered » This shows that the crystal lattice of normal silicon carbide is destroyed, and that the spaces between the individual atoms changed to have" :

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The crystals of silicon carbide with boron in solid solution can be formed in two ways. Once silicon carbide is recrystallized in the presence of boron, or the crystals are formed directly from a mixture that has silicon _{carbide-forming constituents, namely SiO 2} and carbide, as well as the desired proportion of boron. Thermistors made of silicon carbide with boron in solid solution B values in the range from 1200 ° K to around 1800 ° K. ■

Thermistors made of silicon carbide with boron in solid solution have the advantage that the electrical properties do not change significantly with small changes in the boron content. For example, 1 to lOfo borates Mixture added, prior to formation of the crystals by .recrystallization, then the resulting crystals differ in their resistance at tree temperature only very little. The addition of boron results in a Bcr content of about 1 to 3 percent by weight.

Example I.

A pair of tungsten electric wires with approx 0.125 mm in diameter were welded to the ends of Hickel cables with their ends by point welding larger diameter, and in between a crystal of compensated silicon carbide of about -

a2 2

0.7 $ ^ -. And a thickness of 0.25 ium, the larger surfaces of the crystal touched the electrical lines.

Then one let an alternating current of 2.5 Amp. And 6-8 Toit through the pipes until this is about a temperature of 1950 ° C, and this temperature was maintained for about 5 seconds in order to connect the lines to the To weld crystal. Then the device was left to cool down, and to the electrical lines, in the vicinity

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-8th-

of the crystal, were globules of a ceramic cement installed in order to strengthen the whole.

The thermistor produced in this way had a B value of 1860 ⁰ K. "

Example II

Am pair of tungsten electrical wires with one Diameters of about 0.125 mm were made at their ends by spot welding to the ends of Ixekel cables connected with a larger diameter, and it became a * Crystal with the same dimensions as in I. Silicon carbide in solid solution with boron in between, the larger surfaces in contact with the crystal were. The proportion of boron was about three percent by weight. The crystal was made by spring action • the electrical lines held.

Then the lines were connected to an alternating current of 2.5 Amp. and heated 6 to 8 volts to about 1950 ° G, and that heat was held for about 5 seconds to weld the leads to the crystal. Then the whole thing happened cooled, and there were near the crystal to the κ ducts attached spheres of ceramic cement to increase the strength of the whole. -

The thermistor had a 3 value of 1500 ° K.

The amount of elements of group IIIA - VA in the According to the invention, silicon carbide crystals can be up to the weight of the crystal.

According to the invention, electrical lines of very specific materials are used. Lines are best

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made from essentially pure tungsten and from pure tantalum. However, tungsten-tantalum alloys can also be used, optionally with other alloy metals.
Hhenium, molybdenum, and iridium are also useful, as are bise, cobalt, mickel, ehodium, and platinum. However, if the latter metals are used, then the
Some free silicon can be added in the space,
because sonat forms a graphite layer between the metal and the crystal, which weakens the bond.

For the purpose of forming a thermistor,.; ·· the electrical _Λ

Lines are attached to the opposite, -! Pools of the crystal. But the lines can also be attached to the opposite edges of the crystal or to isolated locations on a surface of the crystal. In the composition of the thermistor, the crystal is preferably held by iTederwirkung of the electric wires, so that no special supporting structure is present, 'could contaminate the ien thermistor.

Patent claims

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80 9 80 2/0 5 01

Claims (9)

1) Thermistor, characterized in that it consists of a single crystal consists of pure silicon carbide, or of a silicon carbide that is combined with an element of group IIIA and VA is modified, and that the ' electrical lines are only connected by fusing to isolated points of the crystal. 2) thermistor according to claim 1, characterized in that that the electrical lines consist essentially of pure tungsten. 3) thermistor according to claim 1, characterized in that the .electric lines made of a tungsten-tantalum alloy exist. 4) thermistor according to claim 1, characterized in: ^ that the electrical lines consist of essentially pure tantalum. 5) thermistor according to claim 1, characterized in that the crystal made of silicon carbide with boron in solid Solution consists, wherein the proportion of boron is about 1 $ to about 5 $ of the weight of the silicon carbide. 6) Thermistor according to claim 1, characterized in that the crystal consists of colorless silicon carbide and has a size of. about .0,75 μ χ 0.25 mm Diokeyund that electrical with insulated parts of the crystal '■ lines of tungsten with a diameter of about "0.075 mm ausschliesslioh connected by fusion. are. 809802/0501 - li - 7) 'Thermistor after. .Claim. 6, characterized in that that the isolated areas of the crystal lie on its larger surfaces. 8) Thermistor according to claim 5> characterized, that the proportion of boron is about 3 percent by weight ", 2 and the G size of the crystal about 0.75 mm 0.25 mm Thickness is, and that the "two electrical wires made of tungsten ", have a diameter of 0.075 mm and exclusively by fusing with isolated parts of the crystal. " 9) thermistor according to claim 8, characterized in that ' that the isolated points are on the opposite larger surfaces of the crystal. 809 802/0501