JP2789916B2 - Varactor diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a varactor diode, and more particularly to a varactor diode having improved characteristics.

[0002]

2. Description of the Related Art A conventional varactor diode will be described with reference to FIG. FIG. 2 is a sectional view of a conventional varactor diode.

As shown in FIG. 2, a conventional varactor diode has an impurity concentration of 10 ¹⁴ to 10 on an n ⁺⁺ semiconductor substrate 1.
The second operation layer 3b of 10 ¹⁶ / cm ³ and the impurity concentration of 10
^A first operating layer 3a of ¹⁶ to 10 ¹⁸ / cm ³ is formed, and ap ⁺⁺ layer 4 is formed thereon to form a PN junction. Further, an varactor diode is manufactured by forming an insulating film 6 for protecting the surface and an electrode 7 for electrical coupling with the outside. In FIG. 2, reference numeral 5 denotes a depletion layer.

Generally, the junction capacitance C of a diode has the following relationship with the impurity concentration N and the area S. C = K√N · S… formula (K: proportionality constant)

By the way, a conventional varactor diode is:
In order to increase the capacitance change ratio with respect to the voltage, two operation layers having different impurity concentrations are formed (see the first operation layer 3a and the second operation layer 3b in FIG. 2). Then, in the conventional varactor diode, at a low voltage, the depletion layer 5 spreads in the region of the first operation layer 3a, and a large capacitance value as shown in the part A of FIG. On the other hand, at a high voltage, the depletion layer 5 further expands and enters the second operation layer 3b having a low impurity concentration, and the capacitance is reduced by the equation, as shown in part B of FIG. As a result, the capacitance change ratio between the low voltage and the high voltage is seen to increase.

[0006]

The series resistance R of the varactor diode is preferably as small as possible in order to deteriorate the characteristics. The series resistance R is expressed by the following equation with respect to the impurity concentration N and the area S. R = K · √1 / N · S Equation (K: proportionality constant)

In the conventional varactor diode, in order to increase the capacitance ratio, it is necessary to form a second operating layer having a low impurity concentration in addition to the first operating layer having a high impurity concentration.
As a result, the series resistance of the second operation layer increases. For example, according to the formula and the formula, when the impurity concentration of the second operation layer is set to be nine times that of the first operation layer, the change in capacitance is only 1/3, but
On the other hand, the series resistance is 9 times, the rate of increase of the series resistance is larger than the rate of decrease of the capacitance, and there is a problem that the characteristics of the varactor diode deteriorate.

[0008] An object of the present invention is to provide a varactor diode that solves the above problems. Specifically, when the capacitance change ratio is increased, the series resistance is also increased accordingly. However, according to the present invention, the rate of increase in the series resistance can be reduced despite the same capacitance change ratio. It is an object to provide a varactor diode.

[0009]

The varactor diode according to the present invention is characterized in that the structure of the varactor diode is such that the area of the operation layer is reduced in the depth direction of the operation layer, thereby achieving the above object. Things.

[0010] That is, the present invention provides a method for manufacturing an " n ⁺⁺
Forming an operation layer containing impurities and forming a p ⁺⁺ layer on the operation layer;
In form and becomes varactor diode, wherein the selected portion between the semiconductor substrate and the active layer formed thereon to form an insulating layer, the <br/> operation in the depth direction of the active layer A varactor diode characterized in that the area of the layer is reduced.

[0011]

Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of a varactor diode according to an embodiment of the present invention. The varactor diode has an insulating layer 2 formed on a selected portion of an n ⁺⁺ semiconductor substrate 1, and the semiconductor substrate 1 and the insulating layer And the impurity concentration is 10 ¹⁶ to 10 ¹⁸ / cm ³
Is formed. Further, a p ⁺⁺ layer 4 is formed on the operation layer 3, and an insulating film 6 for protecting the surface and an electrode 7 are formed thereon to form a varactor diode. In FIG. 1,
5 is a depletion layer.

According to the present invention, in order to increase the capacitance change ratio,
A method is used in which the area of the operation layer 3 is reduced from halfway in the depth direction. At a low voltage, the depletion layer 5 spreads over a region where the area of the operation layer 3 is large, and a large capacitance value as shown at A in FIG. 3 is obtained. , And the capacitance is reduced by the above equation, as shown in part B of FIG. As a result, the capacitance change ratio between the low voltage and the high voltage also increases.

In the capacitance-voltage characteristics of this varactor diode, the capacitance value at a low voltage is approximately proportional to the area of the p ⁺⁺ layer 4, but the voltage increases and the depletion layer 5
When it spreads out, the capacitance value decreases sharply in proportion to the area of the operation layer 3 approximately between the insulating layers 2, and the capacitance ratio increases.

According to the above formulas and formulas, when the change in capacitance is reduced to 1/3 by reducing the area of the operation layer 3 to 1/3, the series resistance is tripled, and the same capacitance as that of the conventional varactor diode is obtained. Can be made smaller than the increase rate of the series resistance of 9 times to obtain the variation of In other words, in order to make the capacitance fluctuation 1 / N times, in the conventional varactor diode, the series resistance has been increased by N ² times, but in the varactor diode of the present invention, it can be suppressed by the N times increase in the series resistance. Have the advantages that can be.

[0015]

As described in detail above, the present invention reduces the area of the operating layer in the depth direction, thereby obtaining a capacitance ratio equivalent to that of the conventional varactor diode, and increasing the series resistance of the conventional varactor diode. The effect of reducing the size and improving the characteristics of the varactor diode occurs.

[Brief description of the drawings]

FIG. 1 is a sectional view of a varactor diode showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional varactor diode.

FIG. 3 is a diagram showing a capacitance-voltage characteristic of a varactor diode.

[Explanation of symbols]

Reference ^{Signs List} 1 n ⁺⁺ semiconductor substrate 2 insulating layer 3 operating layer 3a first operating layer 3b second operating layer 4 p ⁺⁺ layer 5 depletion layer 6 insulating film 7 electrode

Claims (1)

(57) [Claims] 1. An operation including an impurity on an n ⁺⁺ semiconductor substrate
Formed by forming a p ⁺⁺ layer on the active layer
In another diode, said semiconductor substrate and on the selected portion between the operation layer formed thereon to form an insulating layer, formed by reducing the area of the active layer in the depth direction of the active layer A varactor diode, characterized in that: