JPH11261082A - Voltage control variable capacitor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a parasitic capacitance from being generated at a series connection point between the cathode of a voltage control variable capacitor diode and a direct current blocking capacitor, in a semiconductor integrated circuit as a voltage control variable device composed of a parallel flat-type capacitor as the direct current blocking capacitor and the voltage control variable capacitor diode. SOLUTION: The one electrode 18A of a parallel flat-type capacitor C4A is connected to the cathode 24A of a voltage control variable capacitor diode CD1A confronting it, and the diode CD1A and the capacitor C4A are laid overlapping with each other to constitute a voltage control variable capacitor device, so that a parasitic capacitor where an insulator 16 located between the lower electrode 18A of the capacitor C4A and the semiconductor substrate 12 is made to serve as a dielectric body can be structually removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for application to an oscillation circuit or the like of a radio device or the like, and is a voltage-controlled variable capacitance element in which a DC blocking capacitor and a voltage-controlled variable capacitance diode are formed as a semiconductor integrated circuit. About.

[0002]

2. Description of the Related Art Conventionally, a voltage-controlled variable capacitance diode (also referred to as a varactor diode) has been employed in a voltage-controlled oscillation circuit or the like.

FIG. 2 shows a voltage-controlled variable capacitance diode CD.
1 shows a configuration example of a general Colpitts-type voltage-controlled oscillation circuit 2 in which No. 1 is used.

Here, the Colpitts type voltage controlled oscillation circuit 2 of FIG. 2 will be described first. This Colpitts-type voltage controlled oscillator circuit 2 includes a common collector amplifier circuit 4 including resistors R1, R2, R3, a bipolar transistor Q1, and a DC voltage source V1, and capacitors C1, C
2, a feedback circuit 6 composed of C3, C4, a voltage-controlled variable capacitance diode CD1, and an inductor L1, and a voltage application circuit 8 composed of a resistor R4 and a variable DC voltage source V2.

The voltage of the DC voltage source V1 connected between the collector of the bipolar transistor Q1 and ground (GND) is divided by the resistors R1 and R2 and supplied to the base of the bipolar transistor Q1 as a DC bias voltage. I have. The resistor R3 inserted between the emitter of the bipolar transistor Q1 and the ground is a feedback resistor for DC bias that determines the collector current or the emitter current, and also serves as the load resistance of the common collector amplifier circuit 4.

In the common collector amplifier circuit 4,
Assuming that the DC voltage source V1 is an ideal voltage source, the inductor value is zero, so that the collector of the bipolar transistor Q1 is AC grounded. However, in practice, the impedance of the DC voltage source V1 itself and the DC voltage source V1
, There is an impedance due to the finite number of wirings at both ends of the bipolar transistor Q1, so that a bypass capacitor is often inserted between the vicinity of the collector of the bipolar transistor Q1 and the ground.

One end is connected to the base of bipolar transistor Q1, and the other end is connected to inductor L1 and capacitor C4.
Is a DC blocking capacitor inserted to prevent the base voltage of the bipolar transistor Q1 from being short-circuited to ground through the inductor L1.

A resistor R4 having one end connected to the common connection point of the capacitor C4 and the voltage-controlled variable capacitance diode CD1, and the other end connected to the positive terminal of the variable DC voltage source V2, controls the voltage of the DC voltage source V2. Controlled variable capacitance diode CD
1 and the impedance of the voltage application circuit 8 is increased with respect to the oscillation signal.

The capacitor C4 is a DC blocking capacitor, and the voltage applied from the voltage application circuit 8 to the cathode of the voltage controlled variable capacitance diode CD1 is applied to the inductor L.
1 prevents short circuit to ground.

The Colpitts type voltage controlled oscillator circuit 2 shown in FIG.
, The impedance when the left side is viewed from the base of the bipolar transistor Q1, that is, the capacitor C1,
In a frequency range where the impedance of the series-parallel connection circuit composed of C4, the inductor L1, and the depletion layer capacitance of the voltage-controlled variable capacitance diode CD1 is inductive, the series-parallel connection circuit can be regarded as an inductor.
This is a so-called Colpitts oscillation circuit.

Since the oscillation frequency of the Colpitts type voltage controlled oscillation circuit 2 is determined by the impedance of the series-parallel connection circuit and the capacitors C2 and C3, the voltage of the variable DC voltage source V2 is changed to change the voltage of the voltage controlled variable capacitance diode CD1. The oscillation frequency can be changed by changing the capacitance value of.

In this case, capacitors C1, C2, C3, C4, which are reactance elements for determining the oscillation frequency,
Inductor L1 and voltage-controlled variable capacitance diode CD
The impedance of 1 actually has a loss component, but when the loss is large, the characteristics of the Colpitts-type voltage controlled oscillation circuit 2 such as the noise characteristics and the index of goodness Q are seriously degraded.

The Colpitts type voltage controlled oscillator circuit 2 shown in FIG.
As can be understood from FIG.
D1 is used by applying a DC reverse bias voltage. In order to prevent this bias voltage from affecting other circuits or from being affected by the bias voltage of other circuits, generally, the voltage-controlled variable capacitance diode CD1 is DC blocking capacitor C
4 are connected for use in series.

FIG. 3 shows a cross-sectional structure of a prior art example of a voltage-controlled variable capacitance element 10 comprising a DC-blocking capacitor C4 connected in series with a voltage-controlled variable capacitance diode CD1 formed in a silicon semiconductor integrated circuit. .

In FIG. 3, an N-type silicon semiconductor region 14 is formed on a P-type silicon semiconductor substrate (substrate) 12 by epitaxial growth or the like, and an element such as a transistor is provided inside the N-type silicon semiconductor region 14. It is formed by a process such as doping of impurities.
The N-type silicon semiconductor region 14 in which elements such as transistors are formed is like an island surrounded by the P-type silicon semiconductor substrate 12, and the P-type silicon semiconductor substrate 12 is connected to the lowest potential in the entire circuit, for example, Normally, by connecting to a ground (GND) potential as shown in FIG.
Each element formed inside the silicon semiconductor region 14 is electrically separated (insulated) by the impedance of the reverse bias of the PN connection by the P-type silicon semiconductor substrate 12 and the N-type silicon semiconductor region 14.

The surface of each element including the P-type silicon semiconductor substrate 12 and the N-type silicon semiconductor region 14 is covered with an insulator 16 such as an oxide film. Are formed, and are ohmically connected to conductor wirings 18 and 20 of metal or the like.

The voltage-controlled variable capacitance diode CD1, which is a depletion layer capacitor, uses a P-type silicon semiconductor region 22 formed in an N-type silicon semiconductor region 14 isolated as an island as an anode, and further uses the P-type silicon semiconductor region 22 as an anode.
The N-type silicon semiconductor region 24 formed therein is formed as a cathode.

The DC blocking capacitor C4, which is electrically connected in series with the voltage-controlled variable capacitance diode CD1, comprises a conductor 18, an insulator 26 and a conductor 28 on the insulator 16 on the surface of the P-type silicon semiconductor substrate 12. Is a parallel plate type capacitor. As can be seen from FIG.
DC blocking capacitor C4 which is a parallel plate type capacitor
Is a voltage-controlled variable capacitance diode C as a lower electrode.
A conductor 18 for wiring connected to the N-type silicon semiconductor region 24 serving as the cathode of D1 is used. An insulator 26 as a dielectric is formed on the conductor 18 for wiring, and an upper part is formed on the insulator 26. It is formed by forming a conductor 28 as an electrode.

[0019]

As described above, in the voltage-controlled variable capacitance element 10 according to the prior art, the voltage-controlled variable capacitance diode CD1 and the DC blocking capacitor C4 connected in series to the diode are separated in a plane. It is formed in the position where it was.

However, the voltage-controlled variable-capacitance element 10 of FIG. 3 in which the voltage-controlled variable-capacitance diode CD1 and the DC blocking capacitor C4 are formed at positions separated in a plane.
In the above, a capacitor comprising an insulator 16 existing between a conductor 18 which is a lower electrode of a DC blocking capacitor C4 comprising a target parallel plate type capacitor (target capacitance) and a P-type silicon semiconductor substrate 12 is formed. Parasitic capacitance C
exists as p. The capacitance value of the parasitic capacitance Cp depends on the insulator 2 existing below the lower electrode of the parallel plate type capacitor.
Although it depends on the thickness and relative dielectric constant of No. 6, there is usually a problem that it may be several tens of percent of the target capacity.

Moreover, since the parasitic capacitance Cp is connected to the ground potential via the P-type silicon semiconductor substrate 12,
There is a problem that the capacitor has an extremely large loss.

In addition, a voltage-controlled variable capacitance diode CD
Since the DC blocking capacitor 1 and the DC blocking capacitor C4 are formed apart from each other, there is also a problem that the loss (mainly, parasitic inductance) of the conductor 18 for connecting between them increases.

When the parasitic capacitance Cp exists, as a result, in the Colpitts type voltage controlled oscillation circuit 2 of FIG. 2, the impedance seen from the base of the bipolar transistor Q1 to the left, that is, the capacitors C1 and C1
4. There is a problem that the loss in the impedance of the series-parallel connection circuit including the inductor L1 and the voltage-controlled variable capacitance diode CD1 increases, and the noise characteristics and the like of the Colpitts-type voltage-controlled oscillation circuit 2 deteriorate as described above.

The present invention has been made in view of such a problem, and provides a voltage-controlled variable capacitance element which does not generate parasitic capacitance at a series connection point between a parallel plate type capacitor and a cathode of a voltage-controlled variable capacitance diode. The purpose is to provide.

Another object of the present invention is to provide a voltage controlled variable capacitance element having a very small parasitic inductance between a series connection of a voltage controlled variable capacitance diode and a DC blocking capacitor.

Still another object of the present invention is to provide a small voltage-controlled variable capacitance element.

[0027]

According to the present invention, a parallel plate type capacitor is formed by superposing a parallel plate type capacitor on a cathode of a voltage controlled variable capacitance diode formed on a semiconductor substrate. The parasitic capacitance between the capacitor and the semiconductor substrate is eliminated, and the parasitic inductance between the parallel plate type capacitor and the cathode of the voltage controlled variable capacitance diode becomes extremely small.

[0028]

An embodiment of the present invention will be described below with reference to the drawings. In the drawings referred to below, those corresponding to those shown in FIGS. 2 and 3 are denoted by the same reference numerals or the same reference numerals, and the description thereof will be simplified. In addition, in order to avoid the complexity of posting twice, description will be made with reference to FIGS. 2 and 3 as needed.

FIG. 1 shows a voltage-controlled variable capacitance element 1 formed in a silicon semiconductor integrated circuit according to an embodiment of the present invention.
The cross-sectional configuration at 0A is shown. This voltage-controlled variable capacitance element 10A basically includes a voltage-controlled variable capacitance diode C
D1A, and a DC blocking capacitor (hereinafter, also referred to as a parallel plate capacitor) C4A as a parallel plate capacitor electrically connected in series to the D1A.

In FIG. 1, an N-type silicon semiconductor region 1 is provided on a P-type silicon semiconductor substrate (substrate) 12.
4 is formed by epitaxial growth or the like, and an element such as a transistor is formed inside the N-type silicon semiconductor region 14 by a process such as impurity doping. The N-type silicon semiconductor region 14 in which elements such as transistors are formed is like an island surrounded by the P-type silicon semiconductor substrate 12.
Is the lowest potential in the whole circuit, for example, usually ground (GN
D) By being connected to the potential, each element formed inside the N-type silicon semiconductor region 14 is electrically connected to the reverse bias impedance of the PN connection between the P-type silicon semiconductor substrate 12 and the N-type silicon semiconductor region 14. Separated (insulated).

The surface of each element including the P-type silicon semiconductor substrate 12 and the N-type silicon semiconductor region 14 is covered with an insulator 16 such as an oxide film. (Opening) is formed, and is ohmically connected to the conductor wirings 18A and 20 made of metal or the like.

The voltage-controlled variable capacitance diode CD1A having the capacitance of the depletion layer capacitance at the PN junction has a P-type silicon semiconductor region 22 formed in the N-type silicon semiconductor region 14 isolated as an island as an anode, The N-type silicon semiconductor region 24A formed in the P-type silicon semiconductor region 22 is formed as a cathode.

A DC blocking capacitor C4A, which is a parallel plate type capacitor electrically connected in series with the cathode of the voltage-controlled variable capacitance diode CD1A, has an outer conductor 28 as an upper electrode and a lower side of the outer conductor 28. A conductor 1A as a lower electrode of the DC blocking capacitor C4A, comprising an internal insulator 26 made of a dielectric material disposed and a conductor 18A disposed below the internal insulator 26;
8A is a voltage-controlled variable capacitance diode CD1A.
N-type silicon semiconductor region 2
4A is connected by ohmic connection to the surface of
A is configured to also serve as a cathode electrode.

As described above, the voltage-controlled variable capacitance element 10A
The conductor 18A as one electrode of the parallel plate type capacitor C4A is connected to the cathode (N-type silicon semiconductor region) 24A of the voltage control variable capacitance diode CD1A so as to face the same, and the voltage control variable capacitance diode CD1A and the parallel plate type capacitor are connected. Since the C4A and the C4A are formed so as to be overlapped with each other, the shape can be reduced in a plan view as compared with the voltage controlled variable capacitance element 10 of FIG. In addition, as described with reference to FIG. 3, the parasitic capacitance Cp having the conductor 18 as the lower electrode of the parallel plate type capacitor C4 and the insulator 16 between the silicon semiconductor substrate 12 as a dielectric is structurally (essentially). Can be removed. Furthermore, since the electrode of the cathode (N-type silicon semiconductor region) 24A of the voltage-controlled variable capacitance diode CD1A is also used as the lower electrode of the parallel plate type capacitor C4A, the series connection impedance between them can be made substantially zero. it can.

By applying the thus formed voltage-controlled variable capacitance element 10A to the Colpitts-type voltage-controlled oscillation circuit 2 shown in FIG. 2, the impedance of the bipolar transistor Q1 as viewed from the base to the left, that is, the capacitors C1 and C4A. Thus, a high-performance oscillation circuit can be realized in which the loss in the impedance of the series-parallel connection circuit including the inductor L1 and the voltage-controlled variable capacitance diode CD1A does not increase and the noise characteristics and the like do not deteriorate.

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0037]

As described above, according to the present invention, since the parallel plate type capacitor is formed by overlapping the cathode of the voltage controlled variable capacitance diode formed on the semiconductor substrate, the shape becomes small. The parasitic capacitance between the parallel plate type capacitor and the semiconductor substrate is eliminated, and the parasitic inductance between the parallel plate type capacitor and the cathode of the voltage-controlled variable capacitance diode becomes extremely small.

When a parallel plate type capacitor is used as a DC blocking capacitor, the loss of the DC blocking capacitor can be reduced, and the inductor between the voltage-controlled variable capacitance diode and the DC blocking capacitor can be almost eliminated. Connection impedance loss can also be reduced. By applying such a low-loss voltage-controlled variable capacitance element to a voltage-controlled oscillation circuit or the like, noise characteristics and the like of the voltage-controlled oscillation circuit can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration of an embodiment of a voltage-controlled variable capacitance element according to the present invention.

FIG. 2 is a circuit diagram showing a configuration example of a general Colpitts type voltage controlled oscillation circuit using a voltage controlled variable capacitance element.

FIG. 3 is a schematic cross-sectional view illustrating a configuration example of a voltage-controlled variable capacitance element according to the related art.

[Explanation of symbols]

2 Colpitts-type voltage-controlled oscillator circuit 4 Collector-grounded amplifier circuit 6 Feedback circuit 8 Voltage application circuit 10 (10A) Voltage-controlled variable capacitance element 12 P-type silicon semiconductor substrate 14 N-type silicon semiconductor region 16, 26 …
Insulators 18, 18A, 20, 28: Conductor (electrode) 22: Anode (P-type silicon semiconductor region) 24 (24A): Cathode (N-type silicon semiconductor region) CD1 (CD1A): Voltage-controlled variable capacitance diode C4 (C4A) ) ... Parallel plate type capacitor (DC blocking capacitor) Cp ... Parasitic capacitance

Claims (1)

[Claims] 1. A voltage-controlled variable-capacitance element in which a semiconductor substrate is provided with a voltage-controlled variable-capacitance diode using a depletion layer capacitance and a parallel plate capacitor connected in series to a cathode of the voltage-controlled variable-capacitance diode. Voltage control, wherein one electrode of the parallel plate type capacitor is connected to the cathode of the voltage controlled variable capacitance diode so as to face the voltage controlled variable capacitance diode, and the voltage control variable capacitance diode and the parallel plate type capacitor are formed in an overlapping manner. Variable capacitance element.