DE2034717A1 - Tuning diode - Google Patents

Description

The invention relates to a hypersensitive tuning diode that of the capacitance curve as a function of that of the diode applied reverse voltage is optimized under specified requirements.

Hypersensitive tuning diodes with a large variation in the Capacity have undesirable turning points in the course of the capacity, depending on the applied reverse voltage. Farther show such diodes operating under the same conditions were produced, large variations in their capacitance values.

A hypersensitive capacitance-voltage curve can be achieved by forming a pn-j junction in a region of falling doping. For this purpose, a base material with doping of one conduction type can be assumed. For example, the use of phosphorus-doped silicon is possible. Let it be assumed that the doping of this base material is N _B. Doping substances are diffused into this base material in a first diffusion, which produce the same conductivity type that the base material already had before. It is therefore possible to use phosphorus, for example, for this first diffusion. A second diffusion with a dopant of the other line type produces a pn junction in the area of falling doping of the first diffusion. For example, it is possible to use boron as the dopant of the other conductivity type.

The known tuning diodes produced by this method have the unfavorable properties mentioned at the beginning.

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It is therefore an object of the present invention to be hypersensitive Specify tuning diodes in which these negative properties are avoided as far as possible by optimizing the construction or design parameters.

This object is achieved in that a semiconductor body with a basic doping concentration N ^ of the one conductivity type in the semiconductor body by means of a first diffusion having a dopant of one conductivity type generated falling doping profile that continues in the semiconductor body a strongly doped zone of the other conductivity type generated by a second diffusion is provided, such that between A pn junction is arranged in the region of the one conduction type and the zone of the other conduction type; is that if you want » ten values

^V 2 ^{+ V} o

A = ________ and r = C ₁ ZC ₂

^y i ^{+ V} o

the ratio W ₁ Zz is chosen so that the parameter a = Ig / l has its maximum possible value that Ν _Λ ζ at most

12 "2
2.84. 10 cm, and that the area of the pn junction is made as small as possible, where ζ is a parameter characterizing the drop in the doping profile with the dimension of a length, V the "offset" voltage, A the voltage swing between the two voltages V ₂ and Y ₁ , r is the capacitance swing between ψ the two capacitances C ₂ and C ₁ , where C ₁ and C ₂ are the capacities of the diode at voltages V ₁ and V ₂ , W _{1 is} the space charge width prevailing at voltage V _{1, and N 0} denotes the doping concentration prevailing at the point of the later pn junction after the first diffusion has been carried out.

The invention eliminates undesirable effects in the capacitance = Stress curve largely avoided. The Kapassi did care from diode to diode are reduced »Furthermore, a prediction of the technical feasibility of certain requirements is

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allows for stanchions to the component. Finally lets on a simple way of providing information about the value of these so-called design parameters.

A further development of the invention is that the Parar meter a ^ 6.1. 10 is.

By this choice of the parameter a can be achieved that in Capacity-voltage curve no turning points occur.

Further features and details of the present invention emerge from the following description of an exemplary embodiment based on the figures.

It demonstrate: Pig . 1: Pig . 2: Pig . 3: Pig . 4:

The doping curve of a diode,

A capacitance-voltage curve,

Fluctuations in capacity values,

The dependence of the parameter a on f «/ z,

Figures 5 and 6; Diagrams to determine the best possible design parameters with given values of A and r.

FIG. 1 shows the dependence of the doping concentration N in a semiconductor body on the spatial coordinate χ. The semiconductor base material has the doping H _fi . Through the first diffusion an area falling Do- generated "orientation, the course of which is assumed to be N (1-a) e ^'B. W here means the Raumladungskoordinate. By the second diffusion was an abrupt pn junction with a doping N. - ^ o ^ formed It is believed that the p-doped left of x lying area strongly in the figure and the area to the right of lying η-doped As a result, upon application of a reverse voltage, the space charge zone... propagates only into the η-conductive area with the falling doping originating from the first diffusion.

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With a sufficient approximation, an exponential course can be assumed:

(1) N (W) = Ν _Ώ + N (1-a) e " ^W / ^e

The space charge coordinate W counts from the pn junction x. the end. The value of

(2) a = N _B / N ₀

is an essential parameter for the manufacture of the tuning diode. N is the doping concentration from the first »diffusion at point x. is generated before the second diffusion is performed. The steepness of the doping profile generated by the second diffusion is characterized by the quantity ζ . For example, for N ^> Ng, with a doping profile according to equation (1), the doping changes by a power of ten over the distance 2.3 ζ.

In the case of an impurity distribution according to equation (1), a theoretical derivation results in the following relationship between the applied Reverse voltage V (calculated as positive in reverse direction) and the space charge width W:

. (3) US. (V + V ₀ ) = 1/2 N _B W ² + N ₀ (1-a) z ² (1 - (1 + W / z) e " ^{W / z} )

Mean:

i- _o = 8.86. 10 "* Asec / Vcm (absolute dielectric constant), t is the relative dielectric constant of the semiconductor material, which is 12 for silicon,

1Q
q = 1.6. 10 Asec (electrical elementary charge), V ₀ is the "offset" voltage and can be found in the journal "JOURNAL OP APPLIED PHYSICS", Volume 38, No. 5, pages 2148-2153. As a first approximation, J _n ~ 0.9 volts + 0.12 volts log ₁₀ N _o / i0 '

, 17th

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Since the space charge width W with the capacity C by the relationship

(4) G =

is connected, where F is the area of the pn junction, If the area F is known, the relationship between the capacitance C and the voltage V is also given by equation (3). A capacitance measurement as a function of the voltage is experimental so that equation (3) can be checked.

The test result is shown in an example in FIG. The solid curve represents the experimentally recorded capacitance-voltage curve, while the crosses reproduce the calculated values according to equation (3). The deviations are smaller than 10 ^ S, so that the theoretical picture with the assumed doping distribution is a good representation of the actual conditions in the finished component. From this can it can be concluded that equation (3) serves as the basis for further considerations for the optimal determination of the design parameters the tuning diode can be used.

It can be shown that no monotonically falling capacitance-voltage dependency is obtained, but rather two turning points occur in this curve when the parameter a <6.1. 10 ^{J is} chosen. As already mentioned, these turning points interfere with the finished component *. It is therefore a value of a = 6.1. 10 to strive for.

It can also be shown that in the manufacture inevitable scatter of the concentration value N by Δ. N lead to the larger the spread of the capacitance, the smaller the value of a. For this purpose, the factor F _{1 of} the relationship in FIG. 3

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Δ C Λ W 4 N
· Ν {- - = F ₁ __ £ with F ₁ (W / z) =

C W ■ N '

with a as a parameter above the normalized space charge coordinate W / z. The values 10, 10 ", 5. 10" ^{5 were} selected for a.

In order to avoid turning points and to avoid capacity spreads as much as possible As can also be seen from FIG. 3, it is expedient to choose a value as large as possible for a.

It is now to be checked what maximum response of a is possible at all, if the following, usually on the component The demands made are to be met!

The capacity swing should be between the voltage values V _{1 and V «}

r ⁼

C (V ₂ )

■ ° ^{1/2 0}

be.

In equation (3), the pair of values T ₁ , W ₁ and the pair of values V ₂ , W ₂ = r. W ₁ introduced and the two equations thus obtained divided by one another. It results *

1/2 -L. (r X ₁ ) ² + f. (p X ₁ ) V ₉ + ■ V 1-a ^{1 1}

( ₅ ) _ £ _JL = A =

_a_ 2 _{+ f (x} 1-a ''

where the abbreviation was used:

(5a) X ₁ = W ₁ A _l ■

(5b) f (X ₁ ) = 1- (1 + X ₁ ). e " ^x 1.

The voltage swing is again designated by A. Equation (5) can be solved for a / (1-a) and yields

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(6) a / (1-a) = (2 / (r ² -A))

A fix. ) - f (r X ₁ )

For given values of r and A, equation (6) gives a relationship between a and X ₁ . This connection is in the Pig. 4 for two pairs of values r, A. These value pairs are:
A = 6.8; r = 15 and A = 4.7; r = 15.

These curves and of course also those for other value pairs r, A have a maximum. The parameter X ₁ is now to be selected in the diode construction so that it corresponds to the maximum value a of a for the curve in question. Will the m

value pair with a_ and x | assigned to the maximum equation (3), since the voltage V ₁ belongs _{to X 1:}

( _{1 0} )
(7) N _o z ² =; ^q - = K

a fixed numerical value K for the product N ζ. In the case of the desired diode, this product has the fixed value K. Nevertheless, N ₀ and ζ themselves cannot be freely selected because the absolute values of N _Q and ζ determine the reverse voltage of the diode. According to IEE] B •• Transactions on Electron Devices ", Volume 10, No. 1, January 1963" | Pages 44 - 51, the product must

(8) N _o zg 2.84. 10 ¹² for 0.1 / um £ ■ ζ «= 1 / um

if it is to be ensured that the reverse voltage is so great that the hyperabrupt doping profile is full of the space charge zone can be detected. If you combine the Equations (8) and (7), then follows as a minimum requirement

³ W ^{for Ζϊ}

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(9) ζ £

2.84. 10 ¹²

If only X ₁ = W ₁ Zz can be freely selected, ζ can be above the value ζ. can be chosen at will. With increasing ζ , however, the value τοη W _{1 increases} . With increasing W _1, the necessary area grows according to equation (4) of the pn junction of the diode "It is desirable to make this surface is not unnecessarily large ssu" Conveniently, 'therefore ζ with a certain safety factor above τοη ζ. chosen, for example ζ = 1.5

The choice of the smallest possible value of ζ and consequently, according to equation (8), the largest possible value τοη 1 and, according to equation (2), the highest possible G-round doping Ng = aN, meets the requirement to achieve a high quality (or a small series resistance) the varactor also very much against »

After determining toh ζ follows Gleieirasg (7), the value I, and thus according to equation (2) I _B = ^a ™ JL AEIE Grundkongentration of the starting material "From the likewise known value sergibt according to equation (5a) of the Eaumlaflwmgsweite to W ₁ = x <| _mia · 2β From this it follows "with a desired capacitance C ₁ from equation (4) the necessary area &<& τ diodes

(10) F = ' ¹ a _} ' ^m

The Besign parameters for the Ab ^ tiEJmsioäe are thus fixed lays.

A high quality of the diode Icatm © rreicht TOrasHj, which is why it consists of epitaxial disks. Mr die Diek © d _Ä « ₄ äer efitak»

? PA 9Z493Z947

table layer and doping Ng.the requirement applies:

^d epi - ^x d ^{+ W} 2 ^{= X} d ^{+ Γ} * ^W 1>

In the following the invention is still to, a numerical example explained in more detail.

A tuning diode with a capacity swing r = 15 between V ₁ = 1 volt and V ₂ = 12 volts is required.

Then, as a first approximation, ν _Λ = 0.9 volts and A = 6.8. With

-3 of these values results from Pig. 4: a _m = 8.3. 10 / at x = 1.31. Pur V ₁ = 1 volt then follows from equations (5a, 5b, 7) for K the value:

K = N ₀ Z ² = 3.31. 10 ⁷ cm " ¹ .

If this result is inserted into equation (9), the result is:

21 · - 0 · 117 / USl

min ♦ '/

It is for ζ including the safety surcharge

chosen: ζ = 0.176 / um

Then it follows: N “= K / z ² = 1.07. 1-0 ~ ¹⁷ cm. ⁵

O Λ λ%

With this Ν _Ώ can be determined: Ν _Ό = & JS. = 8.9. 10 * em. υ υ m ο

Pur the space charge width results from the equation /, (5a) W ₁ = x _1m z = 0.231 / µm.

Pur a required C ₁ = 160 pP follows from equation (10):

P = 34.8. 1Ό " ⁴ " cm ² .

Once this initial data has been determined, it is possible to manufacture the tuning diode:

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In a silicon base material with the doping

ΛΑ * ^ ζ

Ng = 8.9. 10 phosphorus atoms / cm is due to a first Diffusion a falling doping profile according to equation (1)

N (W) = 8.9. 10 ^U + 1.07. 10 ¹⁷ (1 -. 8.3 ~ 10 ³⁾ ~ _e ^{W / O '176}

generated. A heavily p-doped zone is formed by a second diffusion with boron in such a way that the doping profile shown in FIG. 1 with the specified values for N, Ng and ζ arise.

The tuning diode according to the invention has no turning points, since the value of a = 8.3. 10 "'is greater than 6.1. 10. Furthermore, the scattering of the electrical properties of different ones manufactured by the same process are the same Diodes low.

FIGS. 5 and 6 also show diagrams which allow a and x ^ to be quickly determined for given values of A and r * if r is greater than 10. For example, Pig. 5 for A = 6 "8 and r = 15 immediately a = 8.3 · 10"". The dashed line shows the value of a = 6.1. 10 indicated, to be avoided above the turning point in the capacitance-voltage curve of the diode. From Pig. 6 follows for the example case X ₁ = 1.31 »

6 claims
6 figures

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Claims (6)

Claims C 1./Hypersensitive tuning diode, in which the capacitance curve optimized depending on the reverse voltage applied to the tuning diode under specified requirements is characterized in that a semiconductor body with a basic doping concentration N-g of the one type of conduction in the semiconductor body has a falling doping profile generated by a first diffusion with a dopant of one conductivity type, that a heavily doped zone of the other conductivity type produced by a second diffusion is also provided in the semiconductor body, in such a way that between the area of the one line type and the zone of the other line type a pn junction is arranged that when desired Values Λ 2. and r = the ratio W «./ z is chosen so that the parameter a = Ν ,, / ϊΓ has its maximum possible value that N_z J3 O 1? _? O at most 2.84. 10 cm, and that the area of the pn junction is made as small as possible, where ζ is a variable characterizing the drop in the doping profile with the dimension of a length, V _n the ^B offset "voltage, A den (i voltage swing between the two voltages V ″ and V ₁ ,, r the capacity swing between the two capacitances C ″ and C ₁ , where C ₁ and Cg are the capacities of the diode at voltages V ₁ and V ″, W _{1 is} the space charge width prevailing at voltage V ₁ and K denotes the doping concentration prevailing at the point of the later pn junction after the first diffusion has been carried out. VPA 9/493/947 - 12 - 109885/0694 2. tuning diode according to claim 1, characterized in that the parameter a 2: 6.1 .. ^10-3. 3. tuning diode according to claim 1 or 2 »characterized in that ale of the Botierstoff a conductivity type phosphorus is provided. 4. tuning diode according to one or more of claims 1 - 3, characterized in that boron is provided as the dopant of the other conductivity type. 5. tuning diode according to one or more of claims 1-4, characterized in that the tuning diode is incorporated in an epitaxial layer. 6. tuning diode according to claim 5, characterized in that j that the thickness of the epitaxial layer is at least equal to the sum of the thickness of the zone of the other conductivity type and the space charge width at the desired highest reverse voltage applied to the diode. VPA 9/493/947 1098 85/069