JP4798829B2 - Indium phosphorus gun diode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an indium phosphide (InP) Gunn diode used for microwave or millimeter wave oscillation, and in particular, an indium phosphine Gunn diode that realizes improved heat dissipation, improved yield, ease of mounting on a planar circuit, and the like. It is about.
[0002]
[Prior art]
A Gunn diode for microwave or millimeter wave oscillation is usually formed of a compound semiconductor such as gallium arsenide (GaAs) or indium phosphorus (InP). In these compound semiconductors, the mobility of electrons is as high as several thousand cm ² / V · sec at a low electric field, but when a high electric field is applied, the accelerated electrons transition to a band with a large effective mass, and the mobility is high. Decreases, and negative differential mobility is generated in the bulk. As a result, negative differential conductance of current-voltage characteristics appears, resulting in thermodynamic instability. Therefore, a domain is generated and travels from the cathode side to the anode side. As a result of repeating this, an oscillating current (oscillation) is obtained.
[0003]
In the microwave region, the oscillation frequency ft is obtained from the travel distance L and the average electron drift velocity Vd, and ft = Vd / L. In the millimeter wave band, the energy relaxation time, which is the time required for electrons to increase or decrease the energy in the Γ valley, is the main factor that determines the upper limit of the oscillation frequency. The relaxation time constant of gallium arsenide is twice that of indium phosphide, and the cutoff frequencies of gallium arsenide and indium phosphide have been reported to be 100 GHz and 200 GHz, respectively (MAdi Forte-Poisson et al .: Proc. IPRM'89 , p. 551 (1989)). The upper limit of the oscillation frequency of the gallium arsenide gun diode is 60 GHz to 70 GHz at a practical level, and an indium phosphorus gun diode is suitable for a high frequency band such as the 77 GHz band used for automobile radar.
[0004]
In the case of a millimeter-wave Gunn diode, it is necessary to make the travel distance of the domain as extremely short as 1 to 2 μm. Moreover, in order to obtain sufficient oscillation efficiency, it is necessary to set the product of the impurity concentration and the thickness of the traveling space (active layer) of the domain to a predetermined value (for example, 1 × 10 ¹² / cm ² ), Further, since the oscillation frequency is uniquely determined by the thickness of the active layer, the impurity concentration of the active layer becomes considerably high in a high frequency band such as a millimeter wave. The current density in the operating state is determined by the product of the impurity concentration of the active layer and the saturation electron velocity, and in the millimeter wave band, the temperature of the active layer rises due to the increase of the current density, and the oscillation efficiency decreases.
[0005]
Therefore, in order to solve such a problem, the conventional millimeter-wave Gunn diode has a mesa structure, so that the size of the element including the active layer is as small as several tens of μm in diameter. It was assembled in a pill-type package with a heat-dissipating part such as copper with good heat-dissipating efficiency that greatly affects the heat-generating efficiency that affects the most important figure of merit.
[0006]
FIG. 9 is a cross-sectional view of a conventional mesa-type indium phosphorus gun diode 100. A first contact layer 102 made of n + type indium phosphide, n-type (n-type low concentration, hereafter the same) indium is formed on a semiconductor substrate 101 made of n + type (n-type high concentration, the same applies hereinafter) indium phosphide by MOCVD. An active layer 103 made of phosphorus and a second contact layer 104 made of n + type indium phosphorus are sequentially stacked, and a mesa structure is adopted in order to reduce the area of the electron travel space.
[0007]
Thereafter, the back surface of the semiconductor substrate 101 is thinned, the cathode electrode 105 is formed on the back surface of the semiconductor substrate 101, and the anode electrode 106 made of AuGe-based metal is formed on the surface of the second contact layer 104. Then, element isolation is performed to complete a Gunn diode element.
[0008]
The Gunn diode 100 thus formed is assembled in a pill package 110 as shown in FIG. The pill type package 110 has a heat dissipation base electrode 111 and a cylinder 112 made of glass or ceramics as an envelope surrounding the Gunn diode 100. The cylinder 112 is hard-brazed to the heat dissipation base electrode 111. It has a structure. The Gunn diode 100 is electrostatically adsorbed by a bonding tool such as a sapphire material (not shown) and bonded to the heat radiation base electrode 111.
[0009]
Further, the Gunn diode 100 and the metal layer provided at the tip of the cylinder 112 are connected by a gold ribbon 113 by thermocompression bonding or the like. After the gold ribbon 113 is connected, a lid-shaped metal disk 114 is brazed onto the cylinder 112, and the assembly into the pill package 110 is completed.
[0010]
[Problems to be solved by the invention]
However, the conventional indium phosphorous diode 100 is usually formed by a chemical wet etching method using a photoresist as an etching mask in order to obtain the above-described mesa structure. Etching progresses not only in the lateral direction but also in the lateral direction at the same time, and there is a manufacturing difficulty that it is very difficult to control the electron travel space (active layer), and there is a problem that the device characteristics of the Gunn diode vary. .
[0011]
In addition, since the indium phosphorus mesa surface is unstable, there is a problem that the Gunn diode may be burned out due to current concentration on the mesa surface.
[0012]
Further, when assembling the pill type package 110, when the Gunn diode 100 is bonded to the heat dissipation base electrode 111, the bonding tool obstructs the field of view, making it difficult to directly view the heat dissipation base electrode 111. There was also a problem that efficiency was very bad.
[0013]
An object of the present invention is to provide an indium phosphorus gun diode that solves the above-mentioned problems in manufacturing, reliability, assembly, and mounting.
[0014]
[Means for Solving the Problems]
To this end, the first invention comprises a first semiconductor layer made of high-concentration n-type indium phosphorus, an active layer made of low-concentration n-type indium phosphorus, and a high-concentration n-type indium phosphorus on a semiconductor substrate made of indium phosphorus. In the indium phosphorus gun diode in which the second semiconductor layers are sequentially stacked, the first electrode and the second electrode are formed apart from each other on the upper surface of the second semiconductor layer, and the upper surface of the separation region between the two electrodes is formed. A high resistance region is formed by ion implantation at an arbitrary depth between the minimum depth reaching the active layer and the maximum depth reaching the first semiconductor layer, and the first electrode is substantially The diameter was set to 15 μm or slightly smaller, and the second electrode was configured to have a larger area than the first electrode.
[0015]
According to a second invention, in the first invention, the second semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide.
[0016]
According to a third invention, in the first invention, a third semiconductor layer made of high-concentration n-type indium gallium arsenide is further stacked on the second semiconductor layer, and the third semiconductor layer is formed on the upper surface of the third semiconductor layer. The first electrode and the second electrode are formed and configured.
[0017]
According to a fourth invention, in any one of the first to third inventions, the first semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B are diagrams showing the structure of an indium phosphorus gun diode 10A according to an embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view. FIG. 2 is a manufacturing process diagram.
[0019]
First, a manufacturing process is demonstrated according to the content of FIG. An n + type indium having an impurity concentration of 2 × 10 ¹⁸ atom / cm ² and a thickness of 0.5 μm is formed on the semiconductor substrate 11 made of n + type indium phosphorus having an impurity concentration of 3 × 8 × 10 ¹⁸ atom / cm ² by MOCVD. First contact layer (first semiconductor layer) 12 made of phosphorus, active layer 13 made of n-type indium phosphorus having an impurity concentration of 1.5 × 10 ¹⁶ atom / cm ² and a thickness of 1.3 μm, and an impurity concentration of 2 × A semiconductor substrate is prepared in which a second contact layer (second semiconductor layer) 14 made of n + -type indium phosphide having a thickness of 10 ¹⁸ atom / cm and a thickness of 0.3 μm is sequentially stacked ((a) in FIG. 2).
[0020]
Next, a photoresist is patterned on the second contact layer 14 so as to open regions where the cathode and anode electrodes are to be formed, and a metal film made of AuGe, Ni, Au, or the like that is in ohmic contact with the second contact layer 14 (Base electrode layer) is deposited. After removing the photoresist, heat treatment (annealing) is performed, and the cathode electrode 15 and the anode electrode 16 are formed on the second contact layer 14 in a form separated by D = 10 μm ((b) of FIG. 2). Here, the diameter of the cathode electrode 15 is approximately 15 μm or slightly smaller. As shown in FIG. 1, the planar shape of the anode electrode 16 is square at the edge, and the planar shape of the cathode electrode 15 is circular. However, any of an elliptical shape, a substantially square shape, and the like can be selected. Further, the number of cathode electrodes 15 may be two or more as shown in the drawing in order to obtain a desired current.
[0021]
Next, using the cathode electrode 15 and the anode electrode 16 as a mask, the acceleration energy is 30, 100, and 200 KeV, and the dose is 7 × 10 ¹² , 1 × 10 ^13, and 2 × 10 ¹³ / cm ² , respectively. (B) is implanted, and the region from the upper surface of the second contact layer 14 to the bottom surface of the active layer 13 is increased in resistance (insulation) by heat treatment at 400 ° C. to form a high resistance region (insulating region) 17. ((C) of FIG. 2). The high resistance region 17 is formed in a lower layer portion having a gap D = 10 μm between the cathode electrode 15 and the anode electrode 16 described above. Instead of boron (B), oxygen (O), iron (Fe), hydrogen (H) or the like may be ion-implanted to increase resistance.
[0022]
Next, a photoresist is patterned so that a part of the surface of each of the cathode electrode 15 and the anode electrode 16 is opened, and the cathode electrode 15 and the anode electrode 16 are formed in the opening by electrolytic plating or electroless plating. A cathode bump 18 and an anode bump 19 which are conductive protrusions made of Au or the like are deposited as a base electrode (FIG. 2D).
[0023]
The area of the active layer 13 to which the cathode electrode 15 is connected (area of the cathode electrode 16) is set to an area (lateral cross-sectional area) where a predetermined operating current as a Gunn diode can be obtained. That is, the area that can function as a Gunn diode is set. As described above, the diameter of the cathode electrode 15 is approximately 15 μm or slightly smaller, and when a desired current cannot be obtained, a plurality of cathode electrodes 15 are provided. On the other hand, the area of the active layer 13 to which the anode electrode 16 is connected is made sufficiently larger than the area of the active layer 13 to which the cathode electrode 15 is connected, so that the electrical resistance of the semiconductor stacked portion below the anode electrode 16 is reduced. By making it sufficiently smaller than the electric resistance of the lower semiconductor stacked portion, this portion does not function as a Gunn diode, but functions as a resistance portion having a substantially low value, and the anode electrode 16 is substantially directly connected to the first resistance. The contact layer 12 is connected.
[0024]
Next, according to a normal Gunn diode manufacturing process, the back surface of the semiconductor substrate 11 is polished and thinned so that the entire Gunn diode thickness is about 100 μm. Thereafter, if necessary, a metal film (metal) 20 made of AuGe, Ni, Au, Ti, Pt or the like that is in ohmic contact with the semiconductor substrate 11 is deposited on the back surface of the semiconductor substrate 11 and subjected to heat treatment (annealing). Perform ((d) of FIG. 2). Although the metal film 20 formed on the back surface of the semiconductor substrate 11 is not necessarily required, the electrical resistance of the semiconductor stacked portion below the anode electrode 16 can be further reduced.
[0025]
In the Gunn diode 10A of this embodiment formed as described above, the active region 13 made of indium phosphorus functioning as a Gunn diode is separated from the others by high resistance by ion implantation rather than by mesa formation by etching. Therefore, since the surface is unstable, the conventional mesa type problem that the Gunn diode is burned out due to current concentration on the mesa surface does not occur.
[0026]
3 shows a structure in which the Gunn diode 10A of FIG. 1 in which the cathode bump 18 of the cathode electrode 15 and the anode bump 19 of the anode electrode 16 are formed on both sides is mounted on a flat circuit board 31 constituting the microstrip line 30. It is a figure which shows an example. A signal electrode 32 is formed on the surface of a flat plate substrate 31 having a specific resistance of 10 ⁶ Ω · cm or more and a thermal conductivity of 170 W / mK or more, such as aluminum nitride (AlN), and a ground electrode is formed on the entire back surface. 33 is formed. Reference numeral 34 denotes a via hole filled with tungsten, which electrically connects the ground electrode 33 on the back surface and the surface ground electrode 35 formed on the surface.
[0027]
In the Gunn diode 10A, the central cathode bump 18 is bonded to the central signal electrode 32, and the anode bumps 19 of the anode electrodes 16 on both sides are bonded to the surface ground electrodes 35 on both sides. 32A is a bias electrode for supplying a bias voltage to the Gunn diode 10A, 32B is an electrode constituting a resonator by a microstrip line including the Gunn diode 10A, and 32C is a signal output electrode by the microstrip line.
[0028]
The oscillator constituted by the Gunn diode 10A and this mounting structure has a transmission output of 60 mW at an oscillation frequency of 77 GHz when the resonator length (the length of the electrode 32B portion) is 400 μm.
[0029]
In this mounting structure, the Gunn diode 10A is face down, the cathode bump 18 is directly connected to the signal electrode 32, the anode bump 19 is directly connected to the surface ground electrode 35, and the gold ribbon is not used. Thus, the generation of the parasitic inductance that has occurred is eliminated, and an oscillator with little variation in characteristics can be realized.
[0030]
Further, since the heat generated in the Gunn diode 10A is dissipated through the cathode bump 18 and the anode bump 19 to the substrate 31 that also functions as a heat sink, the heat dissipation effect is enhanced. Further, in such a mounted state of the Gunn diode 10A, since the anode bumps 19 of the anode electrode 16 are located on both sides of the cathode bump 18 of the cathode electrode 15, it is possible to prevent an excessive load from being applied to the cathode electrode 15 having a small area. Is done.
[0031]
Furthermore, the Gunn diode 10A of this embodiment can prevent breakdown by making the diameter of the cathode electrode 15 approximately 15 μm or slightly smaller. FIG. 4 shows current-voltage characteristics when the diameter of the cathode electrode 15 is changed to 46 μm, 33 μm, 23 μm, 19 μm, and 15 μm. As an example, when oscillating in the 77 GHz band, since the bias voltage is about 6 V, it can be seen that the cathode electrode diameter needs to be 15 μm or less or smaller to prevent breakdown. This is presumably because the current generated through the deep level and the surface pinning level generated after ion implantation is reduced.
[0032]
FIG. 5 is a view showing a cross section of a Gunn diode 10B according to another embodiment. Instead of the second contact layer 14, indium gallium arsenide (InGaAs) made of n + type In _0.53 Ga _0.47 As and having a thickness of 0.2 μm. ), And operates in the same manner as the Gunn diode 10A of FIG.
[0033]
FIG. 6 is a diagram showing a cross section of a Gunn diode 10C according to another embodiment. Instead of the first contact layer 12, indium gallium arsenide (InGaAs) made of n + type In _0.53 Ga _0.47 As and having a thickness of 0.5 μm. 1), and operates in the same manner as the Gunn diode 10A of FIG.
[0034]
FIG. 7 is a diagram showing a cross section of a Gunn diode 10D according to another embodiment. On the upper surface of the second contact layer 14, indium gallium arsenide (InGaAs) made of n + type In _0.53 Ga _0.47 As and having a thickness of 0.2 μm is used. ) Of the third contact layer 14 ″, and operates in the same manner as the Gunn diode 10A of FIG.
[0035]
FIG. 8 is also a diagram showing a cross section of a Gunn diode 10E according to another embodiment, in which the depth of the high resistance region 17 by boron (B) ion implantation reaches the upper surface of the active layer 13. As described above, when the high resistance region 17 having a high resistance is formed by ion implantation to at least the depth of the interface between the second contact layer 14 and the active layer 13, the part functioning as a Gunn diode is partitioned and separated by the cathode electrode 15. become.
[0036]
【The invention's effect】
As described above, in the Gunn diode of the present invention, the active region made of indium phosphorus functioning as a Gunn diode is not formed by mesa formation by etching but is separated and formed by a high resistance region. Burnout can be prevented.
[0037]
Further, since the ion implantation region when forming the high resistance region is determined in a self-aligning manner using the cathode electrode and the anode electrode as a mask, variation in the characteristics of the Gunn diode can be reduced.
[0038]
In addition, by making the cathode electrode diameter approximately 15 μm or slightly smaller, breakdown during operation can be prevented.
[0039]
In addition, since the cathode electrode and the anode electrode are provided on the same surface, when bumps are provided on them, the heights of the bumps can be set to the same level, so that the mounting posture can be realized face down. For this reason, it is not necessary to assemble into a conventional pill type package, and it is easy to assemble to a flat substrate, and there are great advantages in assembling.
[0040]
Further, since it is not necessary to connect to the microelectrode by a gold ribbon or the like at the time of mounting, there is no occurrence of parasitic inductance, and variations in circuit characteristics due to variations in the length of the gold ribbon can be eliminated.
[0041]
Furthermore, by dissociating the cathode electrode that substantially functions as a Gunn diode into a plurality of parts, the heat radiation efficiency is remarkably improved, and the oscillation efficiency and the oscillation power can be greatly improved.
[Brief description of the drawings]
1A and 1B are diagrams showing an indium phosphorus gun diode according to an embodiment of the present invention, where FIG. 1A is a plan view and FIG. 1B is a cross-sectional view.
FIG. 2 is an explanatory diagram of a method for manufacturing the indium phosphorus gun diode of FIG.
3 is a perspective view of a mounting structure of the indium phosphorus gun diode of FIG. 1. FIG.
4 is a current-voltage characteristic diagram when the diameter of the cathode electrode of the indium phosphorus gun diode of FIG. 1 is changed. FIG.
FIG. 5 is a cross-sectional view of a modification of the indium phosphorus gun diode of FIG.
FIG. 6 is a cross-sectional view of a modification of the indium phosphorus gun diode of FIG.
FIG. 7 is a cross-sectional view of a modification of the indium phosphorus gun diode of FIG.
FIG. 8 is a cross-sectional view of a modification of the indium phosphorus gun diode of FIG.
FIG. 9 is a cross-sectional view of a conventional mesa-type indium phosphorus gun diode.
10 is a cross-sectional view of the mesa structure indium phosphorus gun diode of FIG. 9 incorporated in a pill package.
[Explanation of symbols]
10A, 10B, 10C, 10D, 10E: Indium phosphorous diode 11: Semiconductor substrate, 12: First contact layer, 13: Active layer, 14: Second contact layer, 15: Cathode electrode, 16: Anode electrode, 17: high resistance region by ion implantation, 18: cathode bump, 19: anode bump, 20: metal film 30: microstrip line, 31: flat substrate, 32: signal electrode, 33: ground electrode, 34: via hole, 35 : Surface ground electrode 100: conventional Gunn diode 101: semiconductor substrate 102: first contact layer 103: active layer 104: second contact layer 105: cathode electrode 106: anode electrode 110: pill type Package: 111: Radiation base electrode, 112: Cylinder, 113: Gold ribbon, 114: Metal disc

Claims (4)

On a semiconductor substrate made of indium phosphorus, a first semiconductor layer made of high-concentration n-type indium phosphorus, an active layer made of low-concentration n-type indium phosphorus, and a second semiconductor layer made of high-concentration n-type indium phosphorus are sequentially stacked. In an indium phosphorus gun diode,
A first electrode and a second electrode are formed apart from each other on the upper surface of the second semiconductor layer, and a minimum depth reaches the active layer from the upper surface of a separation region between the electrodes, and the maximum depth is the first depth. A high resistance region is formed by ion implantation at an arbitrary depth until reaching the semiconductor layer of
An indium phosphine diode characterized in that the first electrode has a diameter of about 15 μm or slightly smaller, and the second electrode has a larger area than the first electrode. 2. The indium phosphide diode according to claim 1, wherein the second semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide. A third semiconductor layer made of high-concentration n-type indium gallium arsenide is further stacked on the second semiconductor layer, and the first electrode and the second electrode are formed on the upper surface of the third semiconductor layer. 2. The indium phosphine gun diode according to claim 1, wherein the indium phosphine gun diode is formed. 4. The indium phosphine diode according to claim 1, wherein the first semiconductor layer is replaced with a semiconductor layer made of high-concentration n-type indium gallium arsenide.

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