DE1225765B - Electrical capacitor with voltage-dependent capacitance, consisting of a semiconductor body - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CI .:

HOIg

German class: 21g-10/05

Number: 1225 765

File number: B 56973 VIII c / 21 g

Filing date: March 8, 1960

Opening day: September 29, 1966

The invention relates to an electrical capacitor with voltage-dependent capacitance, which consists of a semiconductor body and in particular for the parametric amplification of microwaves serves.

It is well known that an oscillation circuit with a nonlinear reactance, which is the Apply a first oscillation of large amplitude, tuned to the subharmonics of this oscillation is, a subharmonic oscillation is generated. Used to control the generated subharmonics a subharmonic control signal of low amplitude is additionally applied to the resonant circuit, then Such an arrangement shows amplifier properties and is called a parametric amplifier.

Semiconductors should be used as non-linear reactances or, if the frequencies are high enough, as oscillating circuits with non-linear capacitance also known. The transition layer of a pn semiconductor namely represents a variable capacitance depending on the applied reverse voltage.

Finally it is known that the change in capacitance of a pn junction as a function of the applied bias voltage can be increased by the between the transition and one of the End electrodes located zone of the semiconductor a continuously or according to an older, not to Prior art proposal is given a gradually decreasing cross-section. In both cases, the semiconductor bodies have a distribution gradient of the foreign atoms over them provide the pn junction.

While the greatest difficulties have hitherto been encountered in the manufacture of such semiconductors, semiconductor components with consistent, precisely prescribed characteristics, which is known to be the indispensable prerequisite for semiconductor bodies to be used in the parametric amplification of microwaves, With the teaching of the present invention, it is possible for the first time to achieve these high levels in the simplest possible way To achieve degrees of accuracy, primarily in that the semiconductor body with a certain distribution gradients of the foreign atoms between the two end faces over the pn junction and is provided with a specific shape in the area of the pn junction.

The equivalent circuit diagram of such a semiconductor body shows a variable nonlinear capacitance C to which a resistor R _p is connected in parallel, the combination (C, R _p ) being in series with a resistor R _s . For use as a parametric electrical capacitor with
voltage-dependent capacitance, consisting of
a semiconductor body

Applicant:

Maurice Gilbert Anatole Bernard,

Issy-les-Moulineaux, Hauts-de-Seine (France)

Representative:

Dr. B. Quarder, patent attorney,
Stuttgart, Richard-Wagner-Str. 16

Named as inventor:

Maurice Gilbert Anatole Bernard,
Issy-les-Moulineaux, Hauts-de-Seine (France)

Claimed priority:

France of March 11, 1959 (789 076)

Amplifier, which responds to very high frequencies, must then be assumed that the barrier layer behaves as a pure reactance for the operating frequency ω, i.e. that the impedance of the non-linear capacitor is about -.— ^ -. These, The prerequisite applies regardless of which value the capacitance C assumes, which is the result of the amplification process adjusts. Just the inequality

_1 _{< ω} 1

Rp ■ C Rs' C

must be fulfilled.
1

Around

to keep it small has to go ahead

Rp- C

be set that R _{p represents} a relatively large resistance. This is the case when the pn junction is polarized in the reverse direction. A common value for the resistance R _p is 10 ^s to 10 ⁶ ohms for germanium and 10 'to 10 ⁸ ohms for silicon.

So that - = - ^ - becomes very large, C and R _s K ₅ · c

be very small. As is known, the capacitance C can be brought to approximately 1 pF and the resistance R _s to approximately 1 ohm.

With these conditions we get for - = - ^ a

Κφ · C

Value of about 1 MHz for germanium, which is based on

609 668/326

I 225 765

10 kHz for silicon drops. In contrast, the

Value for

R ₈ -C

several hundred GHz.

The smaller the resistance R _s , the lower the noise figure. The actual amplifier is formed by the reactance of the pn junction and the noise source by the ohmic resistance Rg .

The maximum gain of a parametric amplifier is for the upper sideband for microwaves expressed by the following equation:

/ 2

Here, Z _{1 is} the frequency of the signal to be amplified, / _{2 is} the frequency of the amplified signal, (/ ₂ - / 1) is the frequency of the auxiliary generator whose power is used to amplify the signal at the frequency Z ₁ . χ is a reduced variable that results from the following equation:

χ - μ

with μ =

μ-1

This means that μ is equal to the square root of the ratio of the extreme values that the variable capacitance can assume at the pn junction. The calculated optimal value for this is 1 + Tji; fc = -s — s— τ, - represents the figure of merit of the pn transfer

2πΚ.§ · Cmin

gangs, expressed as the cutoff frequency. The capacitance Cmin is the capacitance of the reverse-biased pn-junction at a voltage that is somewhat lower than the breakdown voltage, ie the maximum permissible reverse voltage.

In the case of a parametric amplifier for the lower sideband, the higher the figure of merit / _c , the higher the frequency of the pn junction, the higher the vibrations.

The above statements clearly show that the gain char acteristics of a parametric amplifier of the product of the minimum capacitance C min and series resistance R _s and depend on the _{proportionality%} nis maximum capacity at minimum capacity. According to Shockley, the minimum capacity C _m { _n is given by the following formula:

1 1

C ■ = KaJ-SV ^ (2)

""" Max

Of this, Vmax is the voltage applied in the reverse direction, subtracting the contact voltage, α the gradient of the distribution of the foreign atoms in the area of the pn junction, S the cross-sectional area of the pn junction and K a constant.

Since the resistance R ₃ lies essentially on one side of the junction, namely in the area of lower conductivity, this area is known to be a. large cross-section assigned to the vicinity of the transition zone. In this case the resistance is not inversely proportional to the junction area, but is determined by the following equation:

Rs =

considered area and b is the radius of the pn junction in centimeters, assumed to be circular. Since ρ = π b ", formula 3 results

Rs =

Here, ρ is the specific resistance in ohms of the. Formulas 2 and 4 show that the capacitance Cmin

is proportional to the cross section of the pn junction, while the resistance R _{8 increases} inversely proportional to the square root of the cross section. The product Rs · C _m i _n varies with the square root of the cross section S, which thus must therefore be low.

To decrease the resistance, you could too the specific resistance ρ can be reduced by increasing the doping of the semiconductor body will; however, this measure requires a reduction in the maximum permissible reverse voltage

ao and has the consequence that the value to be achieved for the minimum capacitance C _m { _{n is} increased.

If low values for the specific resistance ρ and for the cross section S are to be achieved, then it must be avoided that certain limit values are not fallen below, because otherwise the maximum permissible reverse voltage V _max at the pn junction is too low for any application.
The best results achieved so far have been obtained with silicon diodes with diffusion transitions with a distribution gradient of the foreign atoms of 10 ²³ to 10 ²¹ atoms / cm ⁴ . The figure of merit here is 60 to 120 GHz and can also reach 200 GHz, depending on the situation.

The object of the invention is to design the pn junction of a semiconductor body, which serves as a capacitor with voltage-dependent capacitance for parametric amplifiers for microwaves, so that a higher figure of merit is achieved with a lower noise figure compared to the previously known pn junctions in semiconductor bodies becomes, that is, the ratio Cmax '· C _m % _n should reach an optimal value. In addition, a production method is to be described which allows the production tolerances of such semiconductor bodies to be kept within satisfactory limits.

The task is solved by an electrical capacitor with a voltage-dependent capacitance, which consists of a semiconductor body in

its interior a planar pn-junction and a distribution gradient of the foreign atoms between the two electrodes via the pn junction and the one with the pn junction in Connected zone, whose to the pn-

Transition parallel cross-sectional area changes steadily with the distance from the pn junction, whereby according to the invention the distribution gradient of the foreign atoms in the vicinity of the pn junction is 10 ¹⁹ to 10 ²¹ foreign atoms per cubic centimeter and per centimeter and the zone with constant cross-sectional change is conical and the angle Θ between the plane of the pn junction and the surface of the cone is between 1 and 10 ° and the pn junction lies within the conical zone.

The manufacturing process of such an electrical capacitor according to the invention consists in that the semiconductor body consists of a monocrystal

5 6

The curve 1 corresponds to a pn junction, the desired distribution gradient of the foreign atoms in a semiconductor body according to the invention at the transition layer is ordered by pulling at a speed corresponding to a distribution gradient is obtained, and that this semiconductor body to- foreign atoms of 10 ²⁰ atoms / cm ⁴ , a circular closing one is brought into an electrolytic bath with a reverse 5 cross-section of the pn-junction with a voltage in the η range of the radius of 100 μ. is provided, which is arranged in the conical conductor in the immediate vicinity of the pn-over-shaped part of the semiconductor body, to form a constriction in such a way that, as shown in FIG. 1 and 2 is shown. The angle Θ of the semiconductors to the p-area towards a very is a few degrees. In this way, the obtuse cone encompassing the pn junction reaches io the factor
is formed and the pn junction is the desired
Area extension received.

The invention is used below for an off μ =
management example on the basis of the drawings
explained. It shows 15

F i g. 1 shows a semiconductor body according to the invention,

F i g. 2 the charge carrier distribution for both is almost the theoretical optimal value 1 + ] / 2.

Sides of the pn junction, curve 2 corresponds to a pn junction at

F i g. 3 shows a graph in which the same distribution gradient and the same transverse

Capacity C as a function of the applied 20 cut, but with the pn junction in the narrowest

Voltage for different semiconductor bodies is arranged part of the constriction, d. H. in one

is posed. cylindrical profile whose generatrix with the plane

In FIG. 1 the η-region is denoted by 1 and the pn-junction forms an angle of 90 °,

the p-region with 3. The pn-junction is with 2. Curve 3 is plotted for comparison, and

draws. With 4 and 5, the pn junction is on the same scale as curves 1

called dependent contacts. and 2. It shows the change in capacitance as a function of

The p-region 3 is followed by a very shallow voltage from the applied voltage in the case of a “mesadiode” truncated cone or cone, which has a constriction made of silicon, the distribution gradient of which is 10 ²³ to in the η region. The pn junction is located at 10 ²ⁱ atoms / cm ⁴ and the pn junction is not housed in an almost cylindrical profile at the point of the minimum cross section, 30. but in the conical zone, namely there, in the semiconductor body according to the invention where the change in cross section is greatest. In addition, there is also the advantage that this way, a large change in capacitance in the state R _{s of} the pn junction is slightly reduced when the dependence on the applied voltage increases, and the applied voltage increases. The resistance R _s is so that the capacitance value is formed faster than proportional 35 essentially by the p-region, ie with the reciprocal value of the cube root of the by the region where the larger capacitor voltage rises. If there is a pn junction of a coating, the surface of which, as can easily be seen in a semiconductor under the action of a, increases with increasing voltage V , the applied voltage FaIs capacitor is considered so that the resistance i? _s inevitably becomes smaller, the deposits of which are the areas of opposite charge 40 With the above-described electrical condenser on one and the other side of the transition sator, a parametric amplifier can be included, then it is known that the maximum gain and the lowest noise figure on capacitance are reversed be built proportionally with the cubic.

The root of the voltage V changes, where the manufacturing process for such can be assumed that the surface of these pads 45 electrical capacitor with non-linear capacitance remains constant, while the spacing of the pads according to the invention is as follows:
the above law follows. A semiconducting substance, preferably Ger-If the pn-junction, as in Fig. 1 and 2 manium, is shown for the production of a monocrystal, is used in the conical zone of the which has two regions, namely an n-region semiconductor body, the generatrix of which has a 50 and a p-region. Provided that the Winekl Θ forms with the plane of the pn-junction, the transition is made in the direction from ρ to η, which is very small, then the production steps are increased as follows:
Voltage V is a reduction in the surface area of the

Capacitor deposits, the greater the distance between the deposits 1. J _n the germanium bath becomes a certain proportion

is, while the surface of the other condensate 55 of foreign atoms of the acceptor type such as indium

at the same time increases slightly. Introduced at the _o t _he gallium, to a semiconductor region

Semiconductor body according to the invention results from the type ρ with certain specific resistance

accordingly to obtain a reduction in the surface area of the stand.

Capacitor charge if the distance between "_. ,. .,,. ,, _. ,

its coverings is enlarged, proportionally 60 ² · ^Drag * ^emes monocrystal in the p-area with it

with the cube root, which means that a capacity ^emerge marveled at ^Lan B ^e ·

Reduction is connected faster than that by 3. As the monocrystal continues to pull

_i _ will, possibly to an increasing extent, the

the law V ^{s is} given. This increasing proportion of donor foreign atoms like

Non-linearity of the change in capacitance as a function of 65 ■ Antimony or arsenic added to the tape

The ability of the applied voltage to change clearly from type ρ to type η, see above

the comparison of curves 1 and 2 of FIG. 3 shows that a certain specific resistance in the

which have been determined empirically. η area is achieved.

Claims (1)

7 8 4. Continuation of the pulling of the monocrystal to characteristics of the semiconductor according to the invention: to achieve a certain length of resistance in the n-range. direction of flow [R _s ] 0.6 ohms 5. Divide the monocrystal into several cylinders. Minimum capacity [Cmin] 0.25 pF • see parallelepipedic rods with a low negative figure of ⁵ figure of merit [f _c ] 1000 GHz. measurements using a saw or an Ultra claims: sound system, each of these chopsticks having a., ",,.,". , contains pn junction. The length of these rods Jr .. Electric capacitor with voltage is 2 or 3 mm, and its cross-section is dependent on capacity, consisting of a half of the order of 0.5 mm ² . ¹⁰ kiterkorper, which inside a flat shaped pn junction and a distribution 6. Solder the 4 and 5 gradients of the foreign atoms between the two, which are free of the barrier layer to these chopsticks. Has electrodes over the pn junction and 7. Coating of the contacts 4 without a barrier coating, the one with the pn junction in connection and 5 with a protective varnish. The rods * 5 have a standing zone whose cross-sectional areas, which are parallel to the pn junction, are brought into an electrolytic bath, and are then subjected to a selective electrolytic treatment that changes the distance from the pn junction. The denotation that the distribution process consists in the fact that the semi-conductor stretched in the reverse direction of the forward gradient of the foreign atoms in the vicinity with its transition? 2 ° of the pn junction 10 ¹⁹ to 10 ²¹ foreign atoms per resistance bridged by the electrolyte cubic centimeters and per centimeter that is, which means that the various points of the semi- the zone with constant cross-sectional change are more or less shaped, depending on the shape and the angle Θ between working conditions to be attacked, at the level of the pn-junction and the cone jacket where the conductivity of the electrolyte is a ² 5 between 1 and 10 ° and that the pn-overpart plays a role. . gang lies within the conical zone. . 2. Electrical capacitor according to claim 1, characterized by a suitable choice of the electrolyte, the time that the conical action of the electrolysis and the current strength-shaped part of the semiconductor body in the direction, it is possible in this way, a pn junction 3 ° des A further part is connected to the current to maintain its specific cross-section, which steadily increases in a conical cross-sectional area,
shaped zone with an optimal point angle is arranged. . Capacitor according to at least one of the following are the most important Proverbs 1 and 2, characterized in that the dimensions, the setting specifications and the characteristics of a pn semiconductor body is cut from a monocrystal according to the, which is cut by drawing in one of the invention angsgsbsn wsrdsn, which can be used for the paramstric desired distribution gradient of the external gain bsi microwaves. atoms of the pn junction is obtained, and that it is atDimensions of a semiconductor rod: 40 closing in an electrolytic bath at ambient inverted voltage is brought to in the n-loading Length of the n-region 2 mm _{rich of the semiconductor in the} immediate neighboring length of the p-region 1 mm _{due to the pn} transition to a constriction Diameter of the form such that the semiconductor to the p-region pn junction. 100 μ ₄₅ ^ _{n to a very blunt; the} p _n junction Diameter of the one-encompassing cone and the pn-over- cord approx. 70 to 80 μ _{the desired} surface area is obtained. Angle of inclination about 1 to 10 ₄ _ _{Method according to} claim 3, characterized in that during the pulling of the half Manufacturing _{specifications: 5o conductor} monocrystal of the melt the desired Material of the semiconductor .. Germanium impurities with a to achieve the ge Specific resistance wanted distribution gradients of the foreign atoms of the p-area 0.01 Ohm / cm in the area of the pn-junction Specific resistance speed can be added. in the n-area 0.002 ohm / cm 55 Distribution gradient of the documents considered: Foreign atoms 10 ²⁰ atoms / cm ⁴ German Auslegeschrift No. 1 029 483; Drawing speed 200mm / h German interpretation document S 32747 VIIIc / 21g (loading Electrolytic treatment 5 to 10 mA while announced on October 6, 1955); 2 to 3 hours 6o Austrian patent specification No. 180 958; 2 to 4 mA during "Radio Mentor", 1958, no. 3, pp. 154, 155.
about 1 hour Specific Resistance Older Patents ^Considered: of the electrolyte is greater than 1000 ohms. German Patent No. 1 075 745. A priority document was displayed when the registration was announced. 1 sheet of drawings 609 668/326 9.66 © Bundesdruckerei Berlin