JP2004103819A - Monolithic microwave integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a monolithic microwave integrated circuit in which disconnection is hardly caused in a wiring through an air bridge formed between electrodes having a level difference. <P>SOLUTION: Upon connecting between the anode electrode 6a of a PIN diode 3 formed on a semi-insulating substrate 2 so as to be projected and a signaling electrode 8a for a strip transmission line passage by forming the wiring 7 through the air bridge, the level difference between the electrodes is reduced, the rise-up angle of the wiring 7 through the air bridge is reduced, and a connecting distance is shortened by forming the signaling electrode 8a for the strip transmission line passage on an insulating film 9 laminated on the semi-insulating substrate 2 to restrain the generation of disconnection of the wiring 7 due to the air bridge. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a monolithic microwave integrated circuit used in a microwave band and a millimeter wave band.
[0002]
[Prior art]
With the use of microwave and millimeter-wave bands, passive devices and active devices such as PIN diodes for microwave and millimeter-wave bands will be integrated on semi-insulating substrates in communication devices that use these bands. Monolithic microwave integrated circuits are widely used.
[0003]
The PIN diode is a three-layer diode in which an I (Intrinsic) layer that is a high resistivity region formed of an intrinsic semiconductor is disposed between a P-type semiconductor layer and an N-type semiconductor layer. This diode has a very small series resistance when forward biased and a very large series resistance when reverse biased. Furthermore, since the capacitance between the input and output can be made extremely small, it is formed on a common semi-insulating substrate with other microwave elements as a switching element with good on / off characteristics in the microwave / millimeter wave band. It is used as an integrated circuit.
[0004]
FIG. 2 shows an example of the structure of a conventional monolithic microwave integrated circuit including a PIN diode.
[0005]
In FIG. 2, a semi-insulating substrate 10 is a substrate made of, for example, gallium arsenide (GaAs). A PIN diode 11 composed of an N layer 12, an I layer 13, and a P layer 14 is formed on the semi-insulating substrate 10, and has a protruding shape with a height of about 2 μm on the semi-insulating substrate 10. .
[0006]
In order to supply a signal to the anode electrode 14a of the PIN diode 11, a signal electrode 16a and a ground electrode 16b of a strip transmission line are formed on the upper and lower surfaces of the semi-insulating substrate 10, respectively. The end of the electrode 16a is formed close to the PIN diode 11. Then, the anode electrode 14a of the PIN diode 11 and the end of the signal electrode 16a of the strip transmission line are connected by a wire 15 using an air bridge to form a monolithic integrated circuit.
[0007]
An air bridge (aerial wiring) can reduce a parasitic capacitance that hinders high-frequency operation when forming wiring between elements and electrodes in a microwave integrated circuit.
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional structure, since the height of the PIN diode 11 is about 2 μm, the step between the anode electrode 14a of the PIN diode 11 and the signal electrode 16a of the strip transmission line is large. For this reason, the rising angle of the wiring 15 formed by the formed air bridge becomes steep, and the wiring 15 formed by the air bridge is apt to be disconnected. As a result, the yield at the time of manufacturing the integrated circuit has been affected.
[0009]
The present invention has been made to solve the above problems, and is provided on the same semi-insulating substrate as an upper electrode of a semiconductor element such as a PIN diode formed to protrude on the semi-insulating substrate. An object of the present invention is to provide a monolithic microwave integrated circuit in which a wire by an air bridge between a strip transmission line and a signal electrode is less likely to be disconnected.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a monolithic microwave integrated circuit according to the present invention includes a semi-insulating substrate, a semiconductor device protruding from the semi-insulating substrate, and a semiconductor device provided at an upper end of the semiconductor device. One electrode, an insulating film formed on the semi-insulating substrate, a second electrode formed on the insulating film, and an air bridge connecting the first electrode and the second electrode And a wiring according to (1).
[0011]
According to the present invention, the step is reduced by providing the insulating film below the second electrode, and the wiring by the air bridge hardly breaks.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a monolithic microwave integrated circuit according to the present invention will be described below with reference to FIG.
[0013]
FIG. 1 is a sectional view showing the structure of a monolithic microwave integrated circuit according to the present invention. In the monolithic microwave integrated circuit 1 of FIG. 1, the semi-insulating substrate 2 is a substrate made of, for example, gallium arsenide (GaAs).
[0014]
A PIN diode 3 is formed on a semi-insulating substrate 2 as a microwave semiconductor device. This PIN diode 3 has a structure in which an N layer 4, an I layer 5, and a P layer 6 formed by epitaxial growth on a semi-insulating substrate 2 are sequentially laminated. The projections have a height of about 2 μm. An anode electrode 6a of the PIN diode 3 is formed on the upper end surface of the P layer 6 by depositing gold or the like.
[0015]
On the surface of the semi-insulating substrate 2 on which the PIN diode 3 is formed, an insulating film 9 is formed in proximity to the PIN diode 3. This insulating film 9 is a silicon nitride (Si ₃ N ₄ ) film having a thickness of about 0.3 μm.
[0016]
Further, a signal electrode 8a of a strip transmission line whose end is close to the PIN diode 3 is formed on the insulating film 9, and a grounding of the strip transmission line formed on the back surface of the semi-insulating substrate 2. The strip transmission line 8 is constituted together with the electrode 8b.
[0017]
A wire 7 is formed by an air bridge between the anode electrode 6a of the PIN diode 3 and the end of the signal electrode 8a of the strip transmission line adjacent to the PIN diode 3, and the anode electrode 6a of the PIN diode 3 is stripped. It is connected to the signal electrode 8a of the transmission line.
[0018]
In forming the wiring 7 by the air bridge, first, a pillow-shaped support is formed of, for example, a photoresist between two connecting points, that is, between the anode electrode 6a and the end of the signal electrode 8a of the strip transmission line. Then, a metal is deposited on the support to form a metal wiring. Thereafter, when the support is removed, the anode electrode 6a and the end of the signal electrode 8a of the strip transmission line are bridge-connected by a metal wiring, and the wiring 7 by the air bridge is formed.
[0019]
In the above-described structure, since the signal electrode 8a of the strip transmission line is formed on the insulating film 9, two points connected by the wiring 7 by the air bridge, that is, the anode electrode 6a of the PIN diode 3 and the strip transmission line Of the signal electrode 8a can be reduced. For this reason, the rising angle of the wiring 7 by the air bridge is reduced and the connection distance is also shortened, so that the occurrence of disconnection during and after the formation of the wiring 7 by the air bridge can be suppressed.
[0020]
Further, since the connection distance can be reduced, the influence of the air bridge on the signal due to the inductance of the wiring 7 can be reduced.
[0021]
Further, since the insulating film 9 can be obtained by selectively leaving an oxide film, a nitride film, and the like formed temporarily in the process of forming the PIN diode 3 on the semi-insulating substrate 2, the conventional method can be used. The above-described effects can be obtained without substantially affecting the manufacturing process.
[0022]
In the present embodiment, the electrode formed on the insulating film 9 is the signal electrode 8a of the strip transmission line, but may be constituted by a bonding pad or the like. Although the semiconductor element formed on the semi-insulating substrate 2 is the PIN diode 3 and the upper electrode is the anode electrode 6a, the semiconductor element protruding on the semi-insulating substrate and the upper electrode Is not limited to the configuration of the present embodiment.
[0023]
【The invention's effect】
According to the present invention, it is possible to obtain a monolithic microwave integrated circuit in which disconnection is unlikely to occur in wiring formed by an air bridge formed between electrodes having steps.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a structure of a monolithic microwave integrated circuit according to an embodiment of the present invention.
FIG. 2 is a sectional view showing an example of the structure of a conventional monolithic microwave integrated circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Monolithic microwave integrated circuit 2 ... Semi-insulating substrate 3 ... PIN diode 4 ... N layer 5 ... I layer 6 ... P layer, 6a ... Anode electrode 7 ... Wiring by air bridge 8 ... Strip transmission line 8a ... Strip transmission line Signal electrode 8b of the strip transmission line grounding electrode 9 insulating film

Claims (2)

A semi-insulating substrate,
A semiconductor element protruding from the semi-insulating substrate;
A first electrode provided at an upper end of the semiconductor element;
An insulating film formed on the semi-insulating substrate,
A second electrode formed on the insulating film;
A monolithic microwave integrated circuit, comprising: a wiring by an air bridge connecting the first electrode and the second electrode. 2. The monolithic microwave integrated circuit according to claim 1, wherein the semiconductor element is a PIN diode, the first electrode is an anode electrode of the PIN diode, and the second electrode is a strip transmission line.

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