JPS6046077A - Variable capacitance element - Google Patents

Abstract

PURPOSE:To increase the ratio of capacitance change by constructing an insulating film in a laminated structure of the first insulating film formed on the surface of a semiconductor substrate and the second insulating film formed on the first film. CONSTITUTION:An insulating film 25 for forming a capacity read-out unit 24 is constructed in a laminated structure of the first insulating film 25A formed on the surface of an N type semiconductor region 11 such as an oxidized film (SiO2) and the second insulating film 25B formed on the first film such as a nitrided film (SiN). Thus, when the film 25 of the unit 24 is constructed in a laminated structure, the deterioration of insulation due to small thickness of the film 25A is supplemented by the upper film 25B even if the thickness of the film 25A is formed to be small, and H/L ratio can be increased without deteriorating the insulating property. Particularly, the nitrided film has excellent insulation and excellent masking property against an invasion of organic and inorganic impurities from the exterior. Accordingly, even if the thickness is small, sufficiently large H/L ratio can be obtained even if combined with the oxidized film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable capacitance element capable of obtaining a large capacitance change ratio.

A PN junction diode as shown in FIG. 1 is conventionally known as a variable capacitance element used in electronically tuned radios and the like.

In the figure, 1 is an N-type semiconductor region, 2 is a P-type semiconductor region, 3 is a PN junction, and 4 and 5 are the above regions 1 and 2.
Ohmic electrodes 6 and 7 provided on the electrodes 4 and 5 are lead terminals provided on the electrodes 4 and 5, respectively, and 8 is a depletion layer. In the above configuration, the depletion layer 8 expands and contracts in accordance with the bias voltage applied to the lead terminals 6 and 7, and based on this, the change in capacitance value is read out between the lead terminals 6 and 7. .

By the way, in the variable capacitance element having such a structure, the lead terminals 6 and 7 are used not only as capacitance readout terminals (electrodes) but also as bias voltage application terminals for expanding and contracting the two layers. When a human input signal for increasing the capacitance is applied between the extraction terminals 6 and 7, or when a bias voltage is applied, the depletion layer 8 expands and contracts, resulting in a change in the capacitance value. For this reason, when applied to a tuning circuit, the capacitance value changes depending on the input signal, causing tuning deviation and deterioration of cross-modulation characteristics. That is, since the capacitance changes depending on the input signal and the change curve becomes non-linear, the frequency of the input signal is modulated and a high frequency component is generated.

In order to eliminate such defects, the capacitance readout electrode and the bias voltage application electrode are separated from each other. Figure 2 (
3-terminal MIS type variable capacitance element like aJ
No. 5-120175.

In the same figure, 11 is an N-type semiconductor region + 12A, 1
2B is a P-type semiconductor region, 13 is a PN junction, and 14 is the above P
A dielectric film 15, 16A, 16B, and 17 are provided on the surface of the N-type region 11 between the +-type regions 12A and 128, respectively.
Electrode provided at 4.

18, 19.206'! Each electrode 15. Electrode 16A, 1
6B is a U lead terminal provided on the electrode 17, and 21 is a depletion layer.

The P-type regions 12A, 12B and the electrodes 16A, 16B provided thereon constitute a depletion layer control section, and the insulating film 14 and the electrodes 17 provided thereon constitute a capacitive readout section array.

In the above, the width of the second layer 21 is changed by applying a voltage vB to the via 2 which reverse biases the PN junction 13 between the lead terminals 18 and 19, and changing this voltage. The capacitance (CJ vs. pressure (VJ) characteristics as shown in Figure 2 (bJ) can be obtained by reading from between .20 and 20.
The capacitance is the value at VBL after reverse bias 7, the voltage vB is increased and the threshold voltage VBTl has passed, and the capacitance is the maximum value CmaX and the capacitance in the Mis-C-V characteristics, respectively. The minimum value Cm1n is shown.

Here, in order to increase the capacitance change ratio as a variable capacitance element with the structure of FIG. 2 (aJ), it is necessary to increase the above H/L ratio. A method of reducing the thickness of the 24 insulating films 14, or a method of reducing the carrier concentration of the N-type semiconductor region 11 by 7 points can be considered.

However, as in the latter case, lowering the carrier concentration is not desirable because it leads to a decrease in the Q value. Also, in the former case, as shown in FIG. As t becomes /J1, the H/L ratio on the vertical axis can be increased, and the number of pinholes in the insulating film 14 increases proportionally, so the insulating property of the insulating film 14 increases. It is inevitable that the

The present invention has been made in response to the above problems, and is a variable capacitance element in which a depletion layer control section and a capacitance readout section including a constant capacitance readout electrode are formed on a semiconductor substrate via an insulating film. A variable capacitance element is provided in which the insulating film has a laminated structure of a first insulating film formed on the surface of a semiconductor substrate and a second insulating film formed thereon, thereby eliminating the conventional drawbacks. The purpose is to provide Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a cross-sectional view showing a variable capacitance element according to an embodiment of the present invention. The same parts as in FIG. The fully formed first insulating film 25A, for example, an oxide film (5i02
) and a second insulating film 25B formed thereon, for example, a nitride film (SiN 2 ).

The H level and L level of the H7L ratio are related by the following equation.

H level: L level knee example, dSio2=100 A + dS tN
"" When set to 100 A, the above (17, (2J
(As a result of calculation, the H7L ratio can be obtained as approximately 41@.
Although the H/L ratio is a little lower than the H/L ratio when the
The value is about 5 times larger than that when it is provided alone at 2 U and 1,000 λ.

As described above, by configuring the insulating film 5 of the capacitive readout section column to have a multilayer structure, even if the film thickness of the lower insulating film 25A is set to a small value, the deterioration of insulation due to this will be reduced to the upper insulating film 25B. Since it is compensated for by
You will be able to increase the ratio.

In particular, nitride films have poor insulating properties and also have masking properties against the intrusion of impurities from the outside.
By combining it with an oxide film, a sufficiently large H/L ratio can be obtained even if the film thickness is small.

The thickness of each insulating film can be arbitrarily selected depending on the purpose and application.

As is clear from the above description, according to the present invention, in a variable capacitance element in which a depletion layer control section and a capacitance continuous section including a capacitance read electrode are formed on a semiconductor substrate through an insulating film, Since the insulating film has a laminated structure of the first insulating film formed on the surface of the semiconductor substrate and the second insulating film formed thereon, the conventional drawbacks can be eliminated.

Since the present invention provides a variable capacitance element with a large capacitance change ratio, it can be widely applied to various tuning circuits that require electronic tuning.

[Brief explanation of the drawing]

Figures 1, 2 (a) and 2 (bJ are cross-sectional views and characteristic diagrams showing a conventional example, Figure 3 is a characteristic diagram for explaining the present invention, and Figure 4 is a diagram showing an example of the present invention. 16A, 16B: Bias electrode, 17: Capacitance reading electrode, 21: Depletion layer, B: Depletion layer control section, Sae: Capacitance continuous section, 25, 25A , 25B--Insulating film. Figure 1 112 cape. Dimension 11 F) -H leg-L

Claims (1)

[Claims] 1. A variable capacitance element in which a depletion layer control section and a capacitance continuous section including a capacitance read electrode provided through an insulating film are formed on a semiconductor substrate, wherein the insulating film is formed on a semiconductor substrate. A variable capacitance element characterized in that it has a laminated structure of a first insulating film formed on the surface and a second insulating film formed thereon. 2. The first insulating film is an oxide film, and the second insulating film is a nitride film. The variable capacitance element according to claim 1, characterized in that: