JP4516287B2 - Surface mount gun diode and mounting method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface-mount type Gunn diode used as a microwave or millimeter wave supply source and a method for manufacturing the same.
[0002]
[Prior art]
Gunn diode oscillators have good characteristics in phase noise and 1 / f noise, and have been used as useful sources of microwaves and millimeter waves. Gunn diode oscillators are mainly mounted and used in waveguide circuits, but are not suitable for low-cost mass production. However, recently, an oscillator in which a surface mount type Gunn diode is mounted on a dielectric substrate such as aluminum nitride (AlN) has been developed and attracts attention as satisfying the above requirements (for example, see Patent Document 1).
[0003]
FIG. 7 shows a conventional surface mount type Gunn diode 40. 7A is a plan view, and FIG. 7B is a schematic cross-sectional view of the cc plane of FIG. 7A. The gun diode 40 includes a first contact layer 42, an active layer 43, a second contact layer 44, and a metal layer 45 stacked on the top surface of the gallium arsenide substrate 41, and a circular recess 46 in the center. The metal layer 45 is partitioned into an anode electrode 45A and a cathode electrode 45K by forming the metal layer 45 so as to reach the first contact layer 42, and an Au anode bump 47 that is easily thermocompression-bonded on the anode electrode 45A. The cathode bumps 48 of the same Au are formed on the cathode electrode 45K so as to have the same height.
[0004]
The Gunn diode 40 is set such that the area of the active layer 43 in the partition corresponding to the anode electrode 45A is an area where a predetermined operating current of the Gunn diode can be obtained. In addition, the area of the active layer 43 corresponding to the cathode electrode 45K is set to be 10 times or more the area of the active layer corresponding to the anode electrode 45A, and the electric resistance of the semiconductor stacked portion under the cathode electrode 45K is reduced to the area under the anode electrode 45A. By setting it to 1/10 or less of the electric resistance of the semiconductor laminated portion, this portion is not caused to function as a Gunn diode, but substantially functions as a low resistance.
[0005]
In general, the oscillation efficiency of a Gunn diode is about several percent, and most of the input power becomes heat. Therefore, in order not to deteriorate the performance, it is important to efficiently dissipate the generated heat. For this reason, Gandai Auto mesas generally have a multi-mesa structure formed in several pieces as shown in FIG. In this example, four mesas are arranged in a 2 × 2 matrix.
[0006]
FIG. 8 is a perspective view of a conventional surface mount gun oscillator. A microstrip line 10 is formed on the circuit board 1 and a surface-mounted Gunn diode 40 is mounted. In this configuration, since the Gunn diode 40 as the heat source is on the circuit board 1, it is necessary to use a circuit board material having high thermal conductivity in order to efficiently dissipate heat. In this conventional example, aluminum nitride (AlN) having a thermal conductivity of about 170 W / mK is used as a circuit board material.
[0007]
The microstrip line 10 on the circuit board has a pattern as shown in FIG. 9 and is formed on the circuit board 1 by vapor deposition of, for example, Ti / Pt / Au, and further Au plating is applied thereon. The microstrip line 10 is disposed so as to sandwich the signal line 3, the choke part 4 for applying a DC bias to the signal line 3, the signal electrode 5 connected to the signal line 3, and the signal electrode 5 with a gap therebetween. A pair of ground electrodes 11 and a back open 6 are included. The ground electrodes 11 are connected to the ground plane 8 on the back surface via via holes 12 (FIG. 8 shows the circuit board 1 partially cut away). The mounting of the Gunn diode 40 on the microstrip line 10 is performed by thermocompression bonding so that the anode bump 47 of FIG. 7 is connected to the signal electrode 5 and the pair of cathode bumps 48 are connected to the pair of ground electrodes 11.
[0008]
In actual operation, when a DC voltage is applied to the choke unit 4, a current flows through the path of the signal line 3, the signal electrode 5, the Gunn diode 40, the ground electrode 11, the via hole 12, and the grounding surface 8 on the back surface. Electromagnetic waves (microwaves) are generated. The generated electromagnetic wave propagates through the signal line 3 and is output to the outside. The oscillation frequency can be adjusted by changing the length of the back open 6.
[0009]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-22241
[Problems to be solved by the invention]
However, the above surface mount type Gunn diode and its mounting structure have the following problems. First, when a multi-mesa structure element is thermocompression bonded, thermocompression is easily affected by the surface condition of the contact surface, so that there is a slight difference in the mounting state between each mesa due to variations in height, etc. Become. Secondly, the distance between the electrodes (the width of the recess 46) is short, and the surroundings are not covered with an insulator, so the anode electrode and the cathode electrode are likely to be short-circuited. Therefore, mounting by soldering cannot be performed, and a high-cost mounting method such as thermocompression bonding must be used. Third, in the mounting by thermocompression bonding, the surface where the anode electrode and the cathode electrode are in contact with each other must be exactly the same plane, and even if there is a slight level difference, the characteristics are deteriorated. Therefore, the element mounting structure must be configured such that both electrodes exist on the same circuit board. This means that the heat source of the element is on a dielectric, and a material having high thermal conductivity such as AlN must be used as a circuit board, and a general and inexpensive circuit such as a printed circuit board. Since the substrate cannot be used for this oscillator, it causes high costs.
[0011]
An object of the present invention is to solve the above-described problems, and to provide a surface-mount type Gunn diode that can be mounted by soldering, has a low mounting cost, and has a small characteristic variation. Another object of the present invention is to directly connect one of the electrodes on a metal having high thermal conductivity by using a mounting method in which conditions are gentle with respect to a step between the electrodes.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the present invention includes a first semiconductor layer, an active layer, and a second semiconductor layer that are sequentially stacked on a semiconductor substrate, and a plurality of the active layers function as Gunn diodes. As described above, the second semiconductor layer having a plurality of mesa structures separated from the inner region excluding the periphery by an insulator region that reaches at least the active layer from the surface of the second semiconductor layer, and a voltage applied to the active layer The first electrode on the second semiconductor layer separated and partitioned as the plurality of mesa structures for applying the first, and the second on the second semiconductor layer surrounding the first semiconductor layer separated from the first electrode A surface-mounted Gunn diode having conductive electrodes disposed on the first electrode and the second electrode, respectively, wherein the insulator region includes all of the plurality of mesa structures inside. From continuous structure including The first electrode is composed of a single continuous electrode included inside the insulator region and connected by a metal film on the insulator region. The conductive protruding electrode is provided on the first electrode configured. Further, the conductive protrusion electrodes provided on the first electrode and the second electrode are separated from each other by an insulator region.
[0013]
Further, the surface of the second semiconductor layer is composed of a first semiconductor layer, an active layer, and a second semiconductor layer sequentially stacked on the semiconductor substrate, and the plurality of active layers function as Gunn diodes. For applying a voltage to the active layer, a second semiconductor layer separated and partitioned as a plurality of mesa structures in an inner region excluding the periphery by an insulating region having a continuous structure reaching at least the active layer from A single continuous first electrode formed on the second semiconductor layer and on the insulator region, which is included inside the insulator region and separated and partitioned as the plurality of mesa structures; and A surface mount having a second electrode on a second semiconductor layer surrounding the first electrode separated from the first electrode; and a conductive protrusion electrode provided on the first electrode and the second electrode, respectively. The first power source of the Gunn diode One of the above conductive projections electrodes or conductive protruding electrode on the second electrode to the metal substrate, the other to the metal wiring on the non-metallic substrate, and wherein the connecting by soldering.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the structure of a Gunn diode 20 according to an embodiment of the present invention. 1A is a plan view, FIG. 1B is a schematic cross-sectional view of the cc plane of FIG. 1A, 31 is a cathode bump, and 32 is an anode bump. Four circles indicated by dotted lines in the anode bump 32 in FIG. 1A are the anode electrodes 26, and the dotted lines outside the anode bump 32 indicate the outer periphery of the insulator region 28. FIG. 2 shows a manufacturing process of the Gunn diode 20 having the structure of FIG.
[0015]
A manufacturing process of the Gunn diode 20 will be described with reference to FIG. An n-type gallium arsenide having an impurity concentration of 2 × 10 ¹⁸ atoms / cm ³ and a thickness of 1.5 μm is formed on an n-type gallium arsenide substrate 21 having an impurity concentration of 1 to 2 × 10 ¹⁸ atoms / cm ³ by MBE. First contact layer 22, active layer 23 made of n-type gallium arsenide having an impurity concentration of 1.2 × 10 ¹⁶ atoms / cm ³ and a thickness of 1.6 μm, and an impurity concentration of 1 × 10 ¹⁸ atoms / cm ³ A semiconductor substrate is prepared in which second contact layers 24 made of n-type gallium arsenide having a thickness of 0.3 μm are sequentially stacked.
[0016]
Then, on the second contact layer 24, a photoresist that opens a region where the cathode electrode and the anode electrode are to be formed is patterned to form a metal film made of AuGe, Ni, Au, or the like that is in ohmic contact with the second contact layer 24. To do. After removing the photoresist, heat treatment (annealing) is performed, and the cathode electrode 25 and the anode electrode 26 made of the metal film are separately formed on the second contact layer 24 (FIG. 2A). At this time, the anode electrode 26 is arranged separately in the peripheral cathode electrode 25, and a plurality of anode electrodes 26 are formed to form a multi-mesa structure.
[0017]
Next, the second contact layer 24, the active layer 23, and the gallium arsenide substrate are formed by dry etching such as reactive ion etching (RIE) using chlorine gas or the like using the cathode electrode 25 and the anode electrode 26 as a mask. A part of 21 is removed to surround the anode electrode 26, and a vertical recess 27 is formed (FIG. 2B). In the step of FIG. 2A, patterning is performed so that the recess 27 includes the entire anode electrode 27 and has a continuous structure.
[0018]
Next, the recess 27 is filled by applying polyimide by a spin coat method (FIG. 2C). Further, excess polyimide is removed by dry etching so that the cathode electrode 25 and the anode electrode 26 appear on the surface, thereby forming an insulator region 28 (FIG. 2D). Then, a metal film made of Ti, Pt, Au or the like is formed so as to be included in the insulator region 28 on the surface and to connect all the anode electrodes 26 by a method using a photoresist as in the step (a). As a result, a single anode electrode 29 is formed (FIG. 2E).
[0019]
After the photosensitive polyimide is applied on the entire surface, the polyimide other than the bump forming portion is removed by a photolithography process so that a part of the single anode electrode 29 and the cathode electrode 25 appears on the surface, and the second insulator region 30 is removed. Is formed (FIG. 2F). Finally, the cathode bump 31 is formed on the cathode electrode 25 and the anode bump 32 is formed on the single anode electrode 29 by a plating process (FIG. 2G).
The distance between the cathode bump 31 and the anode bump 32 is sufficiently large so that no short circuit occurs even when solder flows during soldering. In the above description, the cathode and the anode are called for convenience, but there is essentially no difference between them, and a high potential may be applied to either.
[0020]
3A and 3B are diagrams showing the structure of a Gunn diode 20 according to another embodiment, in which FIG. 3A is a plan view, and FIG. 3B is a schematic cross-sectional view of the cc plane of FIG. , 30 is a second insulator region, 31 is a cathode bump, and 32 is an anode bump. The four circles indicated by dotted lines in the anode bump 32 in FIG. 3A are the anode electrodes 26, and the dotted lines outside the anode bump 32 indicate the outer periphery of the insulator region 28. In the embodiment shown in FIG. 1, the cathode bumps 31 are arranged on both sides of the anode bump 32. However, in FIG. 3, one bump is provided. The manufacturing method is the same as that described in FIG.
[0021]
In the above description, the shape and number of bumps and anode electrodes shown in each drawing can be variously changed. Each semiconductor layer may use indium phosphide (InP) in addition to gallium arsenide. The insulator region may use a dielectric having a low dielectric constant and dielectric loss tangent other than polyimide, and the insulator region on the semiconductor side may be formed by increasing the resistance by ion implantation of boron or the like. Absent. The insulator region that separates the semiconductor layers may be any one that reaches the active layer, the first contact layer, or the semiconductor substrate.
[0022]
FIG. 4 is a perspective view of a surface mount gun oscillator on which the surface mount gun diode of the present invention is mounted. FIG. 5 shows the pattern of the circuit board 1. The Gunn diode 20 of the present invention is different from the conventional example, and the Gunn diode 20 of the present invention can be mounted by soldering because the multimesa is integrated into one and the anode electrode and the cathode electrode are separated by an insulator. Since mounting by solder is different from mounting by thermocompression, a slight step on the mounting surface is allowed, so that a mounting structure in which the anode bump 32 is directly connected to the metal heat sink 9 can be achieved as shown in FIG. The Gunn diode 20 is not visible in FIG. 4 because it is connected face down with the heat sink 9). Since heat is dissipated from the anode bump 32 to the heat sink 9 with this structure, the circuit board 1 does not necessarily need to use a board having high thermal conductivity, and may be an inexpensive printed board (nonmetal board). FIG. 6 shows an oscillator when the Gunn diode 20 of another embodiment shown in FIG. 3 is used. At this time, only one circuit board 1 is required, and the mounting structure is simpler.
[0023]
【The invention's effect】
As described above, according to the present invention, the active layer includes a first semiconductor layer, an active layer, and a second semiconductor layer that are sequentially stacked on a semiconductor substrate, and a plurality of the active layers function as Gunn diodes. As described above, the second semiconductor layer having a plurality of mesa structures separated from the inner region excluding the periphery by an insulator region that reaches at least the active layer from the surface of the second semiconductor layer, and a voltage applied to the active layer The first electrode on the second semiconductor layer separated and partitioned as the plurality of mesa structures for applying the first, and the second on the second semiconductor layer surrounding the first semiconductor layer separated from the first electrode A surface-mounted Gunn diode having conductive electrodes disposed on the first electrode and the second electrode, respectively, wherein the insulator region includes all of the plurality of mesa structures inside. Including running structure The first electrode is composed of a single continuous electrode that is included inside the insulator region and connected by a metal film on the insulator region. Since the conductive protruding electrode is provided on the first electrode, the mounting state between the mesas can be slightly changed due to height variation or the like, and characteristic variation does not occur. Further, since the conductive protruding electrodes provided on the first electrode and the second electrode are separated by an insulator region, it is possible to perform soldering, which is a low-cost mounting method. In addition, the mounting variation peculiar to the multi-mesa structure and thermocompression bonding can be reduced.
[0024]
Further, the surface of the second semiconductor layer is composed of a first semiconductor layer, an active layer, and a second semiconductor layer sequentially stacked on the semiconductor substrate, and the plurality of active layers function as Gunn diodes. For applying a voltage to the active layer, a second semiconductor layer separated and partitioned as a plurality of mesa structures in an inner region excluding the periphery by an insulating region having a continuous structure reaching at least the active layer from A single continuous first electrode formed on the second semiconductor layer and on the insulator region, which is included inside the insulator region and separated and partitioned as the plurality of mesa structures; and A surface mount having a second electrode on a second semiconductor layer surrounding the first electrode separated from the first electrode; and a conductive protrusion electrode provided on the first electrode and the second electrode, respectively. The first power source of the Gunn diode By connecting one of the upper conductive protrusion electrode and the conductive protrusion electrode on the second electrode to the metal substrate and the other to the metal wiring on the non-metal substrate by soldering, the anode electrode and the cathode A configuration in which the electrode is connected to a circuit board made of another material can be selected, and a mounting structure in which one of the electrodes is directly connected to a metal having high thermal conductivity can be achieved. As a result, an inexpensive circuit board can be used, and the price can be reduced.
[Brief description of the drawings]
FIG. 1 is a plan view (a) and a schematic cross-sectional view (b) of a Gunn diode element of the present invention.
FIG. 2 is a manufacturing process diagram of a Gunn diode element of the present invention.
FIGS. 3A and 3B are a plan view and a cross-sectional schematic view showing another embodiment of the Gunn diode element of the present invention. FIGS.
FIG. 4 is a view showing a mounting structure of a Gunn diode oscillator of the present invention.
FIG. 5 is a circuit board of the Gunn diode oscillator of the present invention.
FIG. 6 is a diagram illustrating a mounting structure showing a modified example of the Gunn diode oscillator of the present invention.
7A is a plan view of a conventional Gunn diode element, and FIG. 7B is a schematic sectional view thereof.
FIG. 8 is a diagram showing a conventional implementation of a Gunn diode oscillator.
FIG. 9 is a circuit board of a conventional Gunn diode oscillator.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Circuit board 2,10 Microstrip line 3 Signal line 4 Choke part 5 Signal electrode 6 Back open 7 Adjustment stub 8 Ground surface 9 on the back 9 Heat sink 11 Ground electrode 12 Via hole 20, 40 Gun diode 21, 41 Gallium arsenide substrate 22 , 42 First contact layer 23, 43 Active layer 24, 44 Second contact layer 25 Cathode electrode 26 Anode electrode 27, 46 Recess 28 Insulator region 29 Single anode electrode 30 Second insulator region 31, 48 Cathode bumps 32, 47 Anode bump 45 Metal film 45A Anode electrode 45K Cathode electrode

Claims (3)

A first semiconductor layer, an active layer, and a second semiconductor layer sequentially stacked on a semiconductor substrate, and at least from the surface of the second semiconductor layer so that the plurality of active layers function as Gunn diodes. Separated as a plurality of mesa structures for applying a voltage to the active layer, a second semiconductor layer in which an inner region excluding the periphery is separated and partitioned as a plurality of mesa structures by an insulator region reaching the active layer A first electrode on the partitioned second semiconductor layer, a second electrode on the surrounding second semiconductor layer separated from the first electrode, on the first electrode, and on the first electrode In a surface-mount type Gunn diode having conductive protruding electrodes respectively provided on the second electrode,
The insulator region is composed of a continuous structure including all the plurality of mesa structures inside,
The first electrode is composed of a single continuous electrode that is included inside the insulator region and connected by a metal film on the insulator region, and is composed of the single electrode. Further, the surface mount type Gunn diode, wherein the conductive protruding electrode is provided on the first electrode. 2. The surface mount type Gunn diode according to claim 1, wherein the conductive projection electrodes provided on the first electrode and the second electrode are separated from each other by an insulator region. A first semiconductor layer, an active layer, and a second semiconductor layer sequentially stacked on a semiconductor substrate, and at least from the surface of the second semiconductor layer so that the plurality of active layers function as Gunn diodes. A second semiconductor layer in which an inner region excluding the periphery is separated and divided into a plurality of mesa structures by an insulating region having a continuous structure reaching the active layer; and the insulation for applying a voltage to the active layer A single continuous first electrode formed on the second semiconductor layer and on the insulator region, which are included inside the body region and separated and partitioned as the plurality of mesa structures, and the first A surface mount gun having a second electrode on a surrounding second semiconductor layer separated from an electrode, and conductive protrusion electrodes respectively provided on the first electrode and the second electrode A diode on the first electrode; A surface mount gun characterized in that either one of the conductive protrusion electrode or the conductive protrusion electrode on the second electrode is connected to a metal substrate and the other is connected to a metal wiring on a non-metal substrate by soldering. How to mount the diode.

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