DE1591231C - Semiconductor diode and use of the semiconductor diode - Google Patents

Description

The invention relates to a semiconductor diode which is designed so that when the diode is operated in the blocking range interference signals caused by parasitic elements can be suppressed. Further uses are such semiconductor diodes indicated.

The semiconductor diode according to the invention can be used, for example, in circuits which are referred to as suppressors or amplitude high-pass filters, i.e. circuits in which one certain threshold voltages exceeding only the voltage portion lying above the threshold value are fed to the output of the circuit target. Such circuits are used, among other things, to shorten the pulse duration of non-rectangular ones Impulses; only the pulse peak, the time base of which is shorter than the signal supplied, is transmitted. Through subsequent amplification, an increase in the pulse edge steepness can be achieved in this way. In known circuits of this type, concentrated diodes having lead wires are used. In the case of high-frequency signals, however, the so-called parasitic elements, i.e. H. the line inductances, the stray capacitances and the junction capacitances present in semiconductor diodes Generates interference signals that appear in the blocking range of the diode at the output of the circuit.

It is true that the capacitances can be reduced to a large extent, which would make it possible to generate a ^{pulse that is only about 5 ps (1 ps = 10 ~ u} s) long. However, a corresponding reduction in the line inductance has not yet been achieved with concentrated elements. Attempts have also been made to utilize the series resonance of the inductances and capacitances connected in series. However, usable results are only achieved up to a pulse duration of about 200 ps and even this only for a relatively narrow frequency range caused by the resonance.

Furthermore, the semiconductor diode can be used advantageously in limiter circuits in which only the voltages which do not exceed a threshold value which is determined by the diode bias voltage appear at the circuit output.

The aim of the invention is to provide a semiconductor diode in which the parasitic elements Interference signals occurring at high frequencies can be suppressed, thereby ensuring satisfactory work such a diode, e.g. B. in circuits for pulse shortening or to increase the pulse edge steepness, in suppressor and limiter circuits, also in the picosecond range will.

This object is achieved according to the invention by a semiconductor diode whose with the Semiconductor body connected electrodes with at least one metallic return conductor input and Form output waveguides which are designed such that they are in the blocking range of the diode as Directional couplers act, causing spurious signals to occur at the output end of the output waveguide is prevented.

Embodiments of the invention are described below with reference to the drawings. It indicates

F i g. 1 a schematic representation of two evenly coupled lines,

2a shows a schematic view of an inventive Diode,

FIG. 2 b shows a schematic illustration of an inventive illustration used for calculating the dimensions Diode,

3a shows a previously known diode suppressor circuit,

FIG. 3b shows the mode of operation of the circuit according to FIG. 3a on the basis of the diode characteristic,

F i g. 4 shows a suppressor circuit in which a diode according to the invention is used.

For a better understanding of the operation of the semiconductor diode according to the invention, first given a brief explanation of the directional coupling effect with the aid of FIG Dimensioning of two adjacent coupled waveguides occurs.

F i g. 1 shows two waveguides 1 and 2, each consisting of a forward conductor I and a return conductor II, which are coupled to one another over the length L. The two return conductors can be earthed as indicated and also be identical. Within the coupling area L, there is a capacitive coupling via the coupling capacitance C ₁₁ and an inductive coupling via the coupling inductance L _K at each point. This is shown schematically in section A for a coupling point.

With a suitable choice of the line parameters, the so-called directional coupling can be achieved, which has the effect that a signal V _x fed to the input E _{x of} the line 1 used as input line appears in the output line 2 only at its line end E ₂ , but the output signal at the line end A ₂ equals zero. The conditions to be met for the directional coupling are derived below, whereby it is assumed, for the sake of simplicity, that the coupled lines _{are terminated without loss and reflection-free with their characteristic impedance Z 1} or Z ₂ and that the coupling is weak, ie

Z ₁ , Z ₂

Z ₁ , Z ₂

■ 5

The voltage V _x generated by the input voltage at point K ₁ generates, via the capacitance C _K in line 2, two currents i ' _k and i' _k flowing from point K ₂ in both directions , the magnitude of which can be determined from the following equation:

l '* l = I' * I « τ '

- V _x .

(U

This approximation formula applies exactly under the assumption that that

J <"C _K

Z _x , z ₂

35

Furthermore, the current /, flowing in the line 1 induces a voltage v _h via the coupling inductance L _K in the line 2, which in turn generates a current /, · in this line, which is directed in the opposite direction to the current i ['. The following applies to the induced voltage:

ν-, = j «> L _K - i _x . (2)

From this it follows
Assumption that

for the current i, under which

j <oL _K » Z ₁ , Z ₂

However, the following applies to the wave impedance Z of a line

/ T

generally Z -y-? · and thus equation (4) can also be written in this form:

2 Z,

(3)

For directional coupling, in which, by definition, the output signal at the end of the line A _{2 should} be zero, the following condition must be met:

Mi =

Z ₁ -Z ₂ - Z _K ,

Since Z ₁ = - ^ - , equating (1) and (3) results in the directional coupling condition:

'j <"C _K

Z _x Z ₂ =

(4)

where Z _{K is} the wave impedance of the line formed from the two conductors I of the coupled lines.

Another analysis of the coupling effects of two coupled lines is given in the article "Transmission-Line Directional Couplers for Very Broad-Band Operation" published by R. Levy in Proc. IEE, Vol. 112, No. 3, March 1965. This is based on the fact that two types of waves can occur on the coupled lines: the common mode wave, the in- phase signals fed through the line ends E _x and E ₂ , and the push-pull wave, the signals of opposite phase fed through these line ends (phase difference 180 ° ) is caused. The investigation of the coupled lines is simplified under this prerequisite, since the analysis of the coupled lines for each of the two wave types can be traced back to the relatively simple equation of a single line, while the approach describing the behavior of the coupled lines with regard to both wave types by superimposing the two resulting equations can be obtained.

From this point of view, if directional coupling conditions are observed and the voltage V _{x is applied} to input E _1, the following equations result for the voltages occurring at the line outputs due to the coupling:

Ku = V _x

= 0,

Jk ₁ ■ sin θ

2 cos θ + Jk ₂ ■ sin (-) 2

2 cos (-) + Jk ₂ ■ sin (-)

where ^ ₁ and k ₂ are values determined by the line parameters, while C-) is the electrical length of the coupled lines, obeying the following equation:

θ =

With

λ = wavelength,
L = length of the coupled lines.

From equation (9) it can be seen that the signal at the output A _{2 is} theoretically zero for all frequencies, the directional coupling effect would thus be frequency-independent. Deviations from this occur primarily due to the losses neglected in the above considerations and, in the case of practical versions, due to the difficulty of adapting the lines for all waves and frequencies without reflection. In addition, it is assumed that no higher order waves occur.

Equations (7) and (8) show that voltages occur at the line ends E ₂ and A _x which have a phase

IO

have a transmission difference of 90 ° and which are dependent on the wavelength and thus on the frequency. The signal V _El reaches its maximum for example for s'mfJ = 1, that is, when the length of the coupled lines is an odd multiple of a quarter of the wavelength λ ; F _t - ₂ , on the other hand, becomes zero when the line length is an integral multiple of half the wavelength.

F i g. 2A shows a schematic representation of a preferred embodiment of the invention Semiconductor diode. This diode consists in principle of a well-known metal semiconductor diode, in which a with one of the surfaces of the semiconductor 23 connected metal electrode 22 with the semiconductor a Schottky barrier forms, while the opposite surface of the semiconductor is an ohmic one Represents contact with a second metal electrode 24. The semiconductor is of the n-conductivity type, the electrode 22 acts as the anode, the electrode 24 as the cathode. In contrast to conventional semiconductor diodes the diode shown in Fig. 2A has a considerable extent L orthogonal to Current flow direction on; it therefore consists of a practically infinite number of parallel acting Diode elements. This diode arrangement is arranged on a metallic base plate 20, the electrodes with respect to the base plate, from which they are separated by an insulating layer 21, at Embodiment superimposed; however, they could also be arranged next to one another. Embodiments, in which the actual diode arrangement between two metallic conductors or Base plates are also possible.

In the setup described, the electrodes form two waveguides with the base plate: The input lead is through the anode electrode 22 and the base plate 20, the output lead through the cathode electrode 24 and the base plate 20 are formed. These two waveguides are such designed and coupled to one another that they act as directional couplers as long as the connecting them Semiconductor diode is operated in the blocking range. The conditions for such behavior were specified in the on the basis of FIG. 1 given explanation of the directional coupling effect. It is essential here, that the parsitary elements are included in the coupled lines when calculating the Line parameters than have to be taken into account.

If the directional coupling conditions are observed, which are expressed in equation (5), a such an arrangement is achieved that as long as the diode operates in the reverse range, from the input line Interference signals coupled into the output line via the parasitic elements of the diode only to one Line end of the output line can be directed, while at the other end of this line no signal occurs.

A detailed description of the embodiment shown in FIG. 2A follows.

The diode arrangement consists of a plurality of layers applied to a metallic base plate 20, which in the exemplary embodiment consists of aluminum. Directly on the base plate is a thin SiO ₂ insulating layer 21 which separates the metal layer 22, which is made of gold, from the base plate. A thin semiconductor layer 23 made of -conducting silicon is applied to this metal layer, which in turn is covered by the metal layer 24, which in turn consists of aluminum. All layers can be produced by known vapor deposition processes using masks and by carrying out etching processes. The materials mentioned represent only preferred examples, which, however, can be replaced by other suitable ones; for example, gallium arsenide, germanium or indium antimonide could also serve as semiconductor material. An essential prerequisite is that a Schottky barrier is formed at the transition between metal (22) and semiconductor (23), while the semiconductor material must make an ohmic contact with the metal layer 24, so that a metal semiconductor diode with the anode electrode 22 and the cathode electrode 24 arises.

The arrangement has an extension L orthogonal to the direction of current flow. The value L is not critical per se; in the exemplary embodiment it is approximately 1 mm. Considerations about the other dimensions, especially the layer thicknesses, are given below.

As already mentioned, the diode electrodes 22 and 24 form two with the base plate over the length L. waveguides coupled to one another. The input line, it corresponds to that in Fig. 1 as a line 1, is composed of the anode electrode 22 and the base plate 20, which is shown in FIG F i g. 1 as line 2 designated pair of conductors from the cathode electrode 24 and the base plate 20 together.

When calculating the characteristic impedances Z ₁ and Z _{2 of} these waveguides and when determining the parameters and dimensions of these lines required to achieve the directional coupling, the characteristic impedance Ζ _{λ of} the waveguide formed by the two electrodes 22 and 24 is also included, as already mentioned, which is referred to below as the coupling line. The directional coupling condition is:

Z ₁ · Z ₂ - Z _K.

The following is a list of some of the equations that are generally valid for determining the wave resistance and are used as the basis for the further calculation; they apply to waveguides that are formed from a conductor of width b and thickness d and from a planar return conductor, for example the base plate.

Z ₀ =

- " U = ^Z o \ ~

Z = U-

= F ₀

b '= b + d.

Jl

b ^ H

(10)

(H)
(12)

(13)

(14)
(15)

ζ, =

(16)

L ₁ = coupling inductance between conductors 20 and 22,

C ₁ = coupling capacitance between conductors 20 and 22.

The wave impedance of the coupling line:

^L k

c _K + c _D

(17)

C'k = (C _D + C _K ),

L ₁₁ = coupling inductance between conductors 22 and 24,

C _K = coupling capacitance between conductors 22 and 24,

C ₀ = junction capacitance of the diode arranged between conductors 22 and 24.

The wave impedance of output line 2:

(18)

Z ₂ =
With

L _K ) (Q + Q)

C ₁ Q

L ₂ = coupling inductance between conductors 20 and 24,

C ₂ = coupling capacitance between conductors 20 and 24.

In the last equation (18), the characteristic impedance of the output line is expressed by the parameters of the input line and the coupling line. This is possible because, for the selected arrangement, the coupling inductance L _{2 of} the output line _{is to be equated with the series arrangement of the coupling inductances L 1} and L _{K of} the input and the coupling line. The same applies to the coupling _{capacitance, ie, C 2} corresponds to the series connection of Cj and C _K.

40

Equations (11), (13), (14) apply approximately to b ' » h.
It means

Z ₀ = wave resistance in the vacuum, μ ₀ = permeability of the vacuum, / (,. = Relative permeability, f ₀ = dielectric constant of the vacuum, e. _R = relative dielectric constant, h = distance of the conductor from the return conductor, b '= effective width of the Conductor, taking into account the coupling from the side surfaces of the conductor to the return conductor, L = coupling inductance between conductors

and return conductor,

C = coupling capacitance between conductor and return conductor.

For the wave resistances of the three interconnected lines of the In the embodiment shown in Fig. 2A, the equations are given below.

The characteristic impedance of input line 1:

Using the notations given in Fig. 2B, by inserting (16), (17), (18) into equation (5):

■ I / o,

(C ₁ + Q) C ₁ ■ C ' _K

_C'K

and further:

fcK'HöO'S) -If- <">

Taking equations (10), (12), (13) and (14) into account, this results in:

1 + -

λ + λ \

h _K

(20)

with h _D = effective thickness of the diode barrier layer (approx. 0.3 μ).

Further calculations, not detailed here, show that this equation, the directional coupling condition includes, for the following dimensions and material constants is met with sufficient accuracy:

/ J ₁ =

4μ

5μ

90 µ

4 (SiO ₂ )

K =

1μ

2μ 2μ

10 (Si)

K =

0.3 µ

₁ shows that the required dimensions can be achieved with known manufacturing processes.

By inserting the determined values into the equations, the characteristic impedances are obtained (16), (17) and (18):

Z ₁ = 8Ω,
Z, = 26 Ω,
Z ' _K = 14 Ω.

For a better understanding of when using the semiconductor diode according to the invention, for example in A suppression circuit achievable advantages is a previously known with reference to FIGS. 3A and 3B Described suppressor circuit, which consists of conventional concentrated components.

Fig. 3A shows the circuit, which essentially consists of a pulse voltage source v _p , a bias battery V _B , the semiconductor diode D and the load resistor R ₁ . The parasitic elements for the diode are indicated by dashed lines: The capacitance C represents the stray capacitance and the junction capacitance of the diode, while the inductance L represents the lead inductances. The battery is polarized such that a bias voltage V _{11 is applied} to the diode D in the reverse direction.

In Fig. 3 B is the operation of the in Fig. 3 A shown circuit based on the current-voltage

209 532/350

Characteristic curve 31 of the diode is shown, the characteristic curve being assumed to be composed of straight sections for the sake of simplicity. The parasitic elements, which are critical only at high frequencies, are initially not taken into account when considering. The pulse voltage v _p = / (O with the maximum value V _p (curve 32) is directed in the opposite direction to the battery bias voltage V _B and is superimposed on it. As long as the voltage value v _{p is} below the bias voltage, ie v _p <V _B , the diode remains blocked ; The current flowing through the load resistor R ₁ is equal to 0. Only during the time period T ₂ , which is shorter than the time base T _{1 of} the entire pulse, the diode becomes conductive, and a resistor R ₁ can be compared to that of the pulse source supplied pulse shortened, but reduced in amplitude voltage signal 33. In a subsequent amplifier circuit, not shown in Fig. 3A, the amplitude can be increased again so that the finally obtained pulse is not only shorter but also has a greater edge steepness .

As already mentioned, this consideration only applies to relatively low frequencies, where the parasitic Elements do not cause significant interfering signals. It should also be mentioned that the in F i g. 3 B shown exactly triangular pulse 33 cannot be realized because the diode characteristics differ from the idealized rectilinear Deviate from the characteristic curve of FIG. 3B. The latter neglect is for a general consideration however permissible.

At high frequencies, the parasitic elements cause a significant change in the output pulse shape. Especially during the time periods in which the pulse voltage of the generator is still below the value of the battery bias, i.e. v _p <V _B , interference signals preceding or following the desired output pulse are generated, which means that a perfect pulse duration reduction from T ₁ to T _{2 is} no longer possible given is. The influences of the individual parasitic elements and their interaction should not be explained in more detail here. As an example, only the obvious influence of the capacitor C connected in parallel to the diode is given, via which a signal is transmitted to the load resistor R ₁ even in the blocking range of the diode.

The interference signals that occur with conventional suppressor circuits, especially at high frequencies are used when using a semiconductor diode according to the invention, as shown in FIG. 2A is suppressed. This is achieved through the directional coupling effect of the diode, which is effective is as long as the diode is operated in the blocking range, d. H. in the time intervals at which the interfering signals are most critical.

In Fig. Fig. 4 shows a suppressor circuit employing a diode of Fig. 2A; it is represented by the electrical equivalent image denoted by 41, in which the conductor pairs of the Waveguides through the strong lines and the practically infinite number in parallel acting diode elements are represented by the conventional diode symbols.

The circuit has an input circuit and an output circuit. The input circuit consists essentially of the waveguide 1 of the diode 41, to which a bias battery V ₁₁ , a pulse source V ₁ and the resistors R ₁ and R _{s are} connected in the manner shown. The output circuit is formed by the waveguide 2 of the diode which is connected to the resistors R ₂ and R _1. Like the aforementioned resistors R ₁ and R ^, these resistors form a reflection-free termination for the waveguides in question. The output signal can be picked up at the connections 42. As long as the diode is operating in the blocking range, the input and output circuits are only connected by coupling the two waveguides, while the circuits in the transmission range are directly connected to one another via the diode. The mode of operation of the circuit is described below both for operation in the stop band and for that in the pass band.

When the pulse voltage source feeds a pulse with a high, but not infinitely large, edge steepness to the end of the line E ₁ , the diode initially remains in the blocking range for a short period of time and, due to the parasitic elements and the coupling between the waveguides 1 and 2, Störsignalc transmitted in the line 2. However, since the diode arrangement is designed as a directional coupler for these signals, with the parasitic elements being part of the coupled lines, the interference signals appear only at resistor R ₂ , but not at output resistor R ₁ . The line inductances of conventional concentrated diodes do not occur in the specified circuit arrangement if it is assumed that the semiconductor diode is connected to the other switching elements via waveguides without reflection.
As soon as the pulse voltage exceeds the reverse bias, the diode works in the conduction range; the parasitic elements are short-circuited and, due to the now low-resistance connection via the diode, the pulse peak exceeding the bias voltage reaches the output resistance R ₁ .

Since the input signal is fed not only to the load resistor R _L , but also to the resistors R ₁ and R ₂ , the amplitude of the output signal is less than the input amplitude; it essentially depends on the ratio of the resistances mentioned and on the internal resistance R ^ of the pulse source. The directional coupling effect is therefore not effective in the pass band of the diode; it starts again as soon as the pulse voltage falls below the bias value.

According to this consideration and according to equation (9), in which the frequency is not directly included, the directional coupling effect for the output A _{2 of} the diode would be independent of frequency. As already emphasized, however, due to losses occurring on the lines and differences in the phase velocities of the common and push-pull waves, which in turn lead to unequal electrical lengths of the coupled lines for these wave types, this is not the case. In practice, however, it can also be in the gigahertz range, ie for pulses from only a few

'Picosecond duration, achieve a wide range. For a frequency range of around an octave the interference signals remain very low.

The output voltage V ₁₁₂ and to a lesser extent

measured the voltage K, ₂ depends, as was already to be expected after considering equations (7) and (8), on the length of the coupled lines or on the frequency. However, this is

formation of the semiconductor diode in the suppressor circuit described of no practical importance.

The in F i g. 4 can also be used as a limiter circuit without significant changes by short-circuiting the output A ₁ and using the resistor R ₁ connected to the line end A _x as the output resistor, from which the output signal supplied by the circuit is tapped and followed by circuits (not shown) can be fed.

The function of a limiter circuit is to feed only the voltage component of an input signal v _p = v (t) fed to the circuit that does not exceed a predetermined threshold value to the circuit output. In conventional arrangements, this is achieved with a suitably biased diode, via which the voltages exceeding the threshold value are short-circuited or diverted. In the case of very short impulses, the parasitic elements of the concentrated diodes previously used become noticeable again in a disturbing manner.

For voltages below the threshold value, the input signal should appear unadulterated at the output; At high frequencies, however, this is prevented by the diode capacitance, which is a shunt to the output resistance. When using a diode according to the invention, the interfering parasitic elements are included in the waveguide system, and the undisturbed signal, which is only changed in amplitude, appears at the output. The output voltage K ₄ is given by equation (8):

2-COS0

In the event that the wave resistance of the lines for the common and push-pull waves at all

Frequencies are the same, K ₄ , = y, regardless of the frequency.

For voltage values exceeding the threshold value, the diode forms a short circuit, so that the Output voltage of the limiter circuit independent of the input voltage to the threshold value is limited.

The semiconductor diode according to the invention has been described using an exemplary embodiment. It it should be noted that the arrangement selected here, its dimensions and materials only represent a preferred example. For example, the invention is not limited to one as for the embodiment selected metal semiconductor diode confined with a Schottky barrier; it could, among other things Diodes with a p-n junction are also used. The use of the inventive Diode is not limited to the suppressor and limiter circuits described.

1 sheet of drawings

Claims (6)

I 59 1 231 claims: 1. Semiconductor diode, characterized in that that the electrodes of the diode connected to the semiconductor body with at least a metallic return conductor to form input and output waveguides which are designed in this way are that they act as a directional coupler in the blocking region of the diode, whereby the occurrence of Interference signals at the output end of the output waveguide is prevented. 2. Semiconductor diode according to claim 1, characterized in that one of the electrodes (22) consists of consists of a metal which is present in the boundary layer of the semiconductor body connected to the electrode (23) creates a Schottky barrier. 3. Semiconductor diode according to at least claim 1, characterized in that the semiconductor body and the electrodes have an extension in a direction orthogonal to the direction of current flow, which for high signal frequencies is in the range of the wavelength of these frequencies. 4. Semiconductor diode at least according to claim 1, characterized in that a metallic Base plate is provided as a return conductor for the input and output waveguides. 5. Semiconductor diode according to claim 4, thereby characterized in that the electrodes are arranged one above the other with respect to the base plate. 6. Use of the semiconductor diodes according to Claims 1 to 5, characterized in that the diode is part of such circuits in which by exceeding a certain threshold value Voltages only the one above the threshold value or only the one below the threshold value Voltage component is fed to the output of the circuit.