JP2009231751A - TWO-WAY SWITCHING ELEMENT COMPOSED OF GaN COMPOUND SEMICONDUCTOR - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a device having a normally-off type, low loss, two-way switching function by a single device. <P>SOLUTION: A two-way switching element includes: an operation layer having a certain conduction type; a first and a second electrodes formed on the operation layer; a first contact layer having an opposite conduction type formed in contact with the first electrode in the operation layer; a second contact layer having the opposite conduction type formed in contact with the second electrode in the operation layer; at least one gate electrode almost symmetrically formed about a center line between the first and the second electrodes through an insulation film on the operation layer; a channel portion formed in the operation layer of a portion corresponding to the gate; and at least one field relaxation layer formed between the first and second n-type semiconductor layers having lower impurity concentration of the opposite conduction type than the first and second contact layers. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a bidirectional switching element using a GaN compound semiconductor.

Nitride compound semiconductors represented by the chemical formula Al _x In _y Ga _1-xy N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, x + y ≦ 1), such as compound wide bands such as GaN compound semiconductors Gap semiconductors have excellent physical properties compared to Si, which is currently the mainstream semiconductor material, such as high breakdown voltage, saturated carrier mobility, and thermal conductivity. Therefore, semiconductor devices for high power or high frequency in high temperature environments. Has attracted attention as a material.

  For example, an AlGaN / GaN heterojunction field effect transistor (HFET) has high carrier density and electron mobility due to a two-dimensional electron gas (2DEG) at the heterostructure interface generated by a piezoelectric field. . This HFET is suitable for application as a high power switching element because of its characteristics such as low on-resistance, high-speed switching characteristics, and high-temperature operation capability. (Non-Patent Document 1)

Usually, an AlGaN / GaN HFET is a normally-on type device in which current flows even when no voltage is applied to the gate, but in a power switching element, in order to ensure safety when the device is destroyed, A normally-off type device in which no current flows when no voltage is applied to the gate is preferable.

  In many applications using semiconductor devices, devices with bidirectional switch functions are required to reduce the number of devices and reduce loss. Bidirectional switching elements are used to realize matrix converters and the like. Is an indispensable device.

  In the current Si-based IGBT and MOSFET, the reverse breakdown voltage cannot be secured due to the structure. For this reason, when a bidirectional switching device is created using a Si-based device, it is necessary to configure the device by combining two IGBTs and two diodes as shown in FIG.

  However, since the loss due to the device is determined by the number of elements through which current passes and the resistance of each element, it is difficult to reduce the loss due to the switching device by the conventional method.

The present invention has been made in view of the above problems, and an object thereof is to realize a normally-off type device having a low-loss bidirectional switch function by one device.

M. Kuraguchi et al., Normally-off GaN-MISFET with well-controlled threshold voltage, International Workshop on Nitride Semiconductors 2006 (IWN2006), Oct. 22-27, 2006, Kyoto, Japan, WeED1-4

  A bidirectional switching element comprising a GaN-based compound semiconductor according to the present invention includes an operation layer having one conductivity type, a first electrode and a second electrode formed on the operation layer so as to be separated from each other, A first contact layer having an opposite conductivity type formed in contact with the first electrode in the working layer; and an opposite formed in contact with the second electrode in the working layer. A second contact layer having a conductivity type; and at least one gate electrode formed substantially symmetrically with respect to a center line between the first electrode and the second electrode via an insulating film on the operation layer; At least one channel portion is formed between the first electrode and the second electrode, and the first contact layer and the second contact are formed in the operation layer corresponding to the gate electrode. Opposite conductivity with lower impurity concentration than layer Bidirectional switching element and a field relaxation layer having a.

In the bidirectional switching element made of a GaN-based compound semiconductor according to the present invention, one gate electrode is formed between the first electrode and the second electrode, and the electric field relaxation layer includes the first It is formed between one contact layer and the channel portion, and between the second contact layer and the channel portion.

In the bidirectional switching element comprising a GaN-based compound semiconductor according to the present invention, two gate electrodes are formed between the first electrode and the second electrode, and the electric field relaxation layer includes two It is formed between two channel portions formed in a portion corresponding to the gate electrode.

Further, in the bidirectional switching element comprising the GaN-based compound semiconductor according to the present invention, the GaN-based compound semiconductor is Al _x In _y Ga _1-xy N (where 0 ≦ x <1, 0 ≦ y <1 0 ≦ x + y ≦ 1).

The bidirectional switching element made of a GaN-based compound semiconductor according to the present invention includes a p-type semiconductor layer, an operation layer stacked on the p-type semiconductor layer, and stacked on the operation layer. An electron supply layer made of a semiconductor material having a wider band gap, a first ohmic electrode and a second ohmic electrode formed on the electron supply layer, the first ohmic electrode, and the second ohmic electrode Between the first gate electrode formed on the electron supply layer, and the first ohmic electrode and the second ohmic electrode, the electron supply layer and the operation layer have a predetermined An opening reaching the p-type semiconductor layer formed at a position is provided with a second gate electrode provided through an insulating film.

In the bidirectional switching element made of a GaN-based compound semiconductor according to the present invention, the p-type semiconductor layer is p-type GaN, the operation layer is undoped GaN or n-type GaN, and the electron supply layer is , Al _x In _y Ga _1-xy N (where 0 <x <1, 0 ≦ y <1, 0 ≦ x + y ≦ 1) layers.

  According to the present invention, since the device is configured using the MOSFET, there is a remarkable effect that it is possible to realize a normally-off type bidirectional switching device with a small loss.

  Embodiments of a bidirectional switching element according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, in each embodiment, the same code | symbol is attached | subjected to the same structure and description is abbreviate | omitted.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view of a bidirectional switching element according to Embodiment 1 of the present invention.
In this bidirectional switching element 10, a buffer layer 102 and an operation layer 104 made of p-type GaN are formed on a substrate 100. A contact layer 120 and a contact layer 122 made of n ⁺ -type GaN are formed on the operation layer 104 at a predetermined distance. On the operation layer 104, ohmic electrodes are in contact with the contact layer 120 and the contact layer 122, respectively. 110 and an ohmic electrode 112 are formed. Further, a gate electrode 114 is formed on the operation layer 104 between the ohmic electrode 110 and the ohmic electrode 112 with an insulating film 116 interposed therebetween. A channel portion 140 is formed in the operation layer 104 in contact with the insulating film 116. Between the channel part 140, the contact layer 120, and the contact layer 122, an electric field relaxation layer 130 and an electric field relaxation layer 132 made of n-type GaN are formed. Here, the gate electrode 114, the insulating film 116, the electric field relaxation layer 130, and the electric field relaxation layer 132 are formed substantially symmetrically with respect to the center line between the ohmic electrode 110 and the ohmic electrode 112.

The bidirectional switching element 10 operates as a normally-off type and is formed substantially symmetrically with respect to the center line between the ohmic electrode 110 and the ohmic electrode 112, so that the two ohmic electrodes are respectively a source electrode or a drain electrode. And can perform high-speed switching operation in both directions.

  In the bidirectional switching element 10, the gate electrode 114, the ohmic electrode 110, and the ohmic electrode 112 are formed by the electric field relaxation layer 130 and the electric field relaxation layer 132 formed between the gate electrode 114, the contact layer 120, and the contact layer 122. Since the electric field concentration between them is relaxed, it has a high reverse breakdown voltage characteristic even when it is off.

FIG. 2 is a schematic cross-sectional view showing a manufacturing process of the bidirectional switching element according to Embodiment 1 of the present invention.
The bidirectional switching element having the above configuration can be manufactured as follows. The growth apparatus was a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, and the substrate was a sapphire (0001) substrate 100.

(1) Epitaxial growth process After introducing the sapphire (0001) substrate 100 into the MOCVD apparatus and evacuating the MOCVD apparatus to a vacuum level of 1 × 10 ⁻⁶ hPa or less with a turbo pump or the like, an inert gas is introduced. Then, the degree of vacuum was set to 100 hPa, and the substrate 100 was heated to 600 ° C. When the temperature is stabilized, while the substrate 100 is rotated at 900 rpm, trimethylaluminum (TMA) as a raw material is introduced into the surface of the substrate 100 at a flow rate of 100 cm ³ / min and ammonia is 12 liter / min, and a buffer made of AlN. Layer 102 was deposited to approximately 50 nm.
Thereafter, the temperature in the apparatus is increased to 1050 ° C. while flowing a flow rate of 12 liter / min of ammonia, and trimethylgallium (TMG) is 300 cm ³ / min and ammonia is flowed on the buffer layer 102 at a flow rate of 12 liter / min. The working layer 104 made of p-type or undoped GaN layer was deposited to 3000 nm. Here, as the p-type impurity, for example, magnesium or the like can be used.

(2) Electric field relaxation layer and contact layer formation step Next, the contact layer 120, the contact layer 122, and the electric field made of n-type GaN doped with n ⁺ type impurities such as Si by a method such as selective regrowth and ion implantation. The relaxation layer 130 and the electric field relaxation layer 132 are formed. (Fig. 2 (b))

(3) Electrode Formation Step Next, the ohmic electrode 110 and the ohmic electrode 112 are formed so as to be in contact with the contact layer 120 and the contact layer 122. Then, the bidirectional switching element 10 as shown in FIG. 1 is formed by forming the gate electrode 114 through the insulating film 116 on the channel portion 140 where the electric field relaxation layer 130 and the electric field relaxation layer 132 are not formed. be able to.
Here, the gate electrode 114 is preferably formed approximately in the middle between the two ohmic electrodes, but is shifted from the center by appropriately setting the impurity density and mobility of the electric field relaxation layer 130 and the electric field relaxation layer 132. It can also be formed in position.

Insulating film 116, the material of the ohmic electrode 110, an ohmic electrode 112 and the gate electrode 114 is not particularly limited, for example, as the insulating film _116, it is possible to use SiO 2, SiN, or the like. Further, Ti / Al or the like can be used for the ohmic electrode 110 and the ohmic electrode 112, and Pt / Au or the like can be used for the gate electrode 114.

(Embodiment 2)
FIG. 3 is a schematic cross-sectional view of a bidirectional switching element according to Embodiment 2 of the present invention.
In the bidirectional switching element 20, a buffer layer 102 and an operation layer 104 made of p-type GaN are formed on a substrate 100. A contact layer 120 and a contact layer 122 made of n ⁺ -type GaN are formed on the operation layer 104 at a predetermined distance. On the operation layer 104, ohmic electrodes are in contact with the contact layer 120 and the contact layer 122, respectively. 110 and an ohmic electrode 112 are formed. A gate electrode 114 and a gate electrode 115 are formed on the operation layer 104 between the ohmic electrode 110 and the ohmic electrode 112 with an insulating film 116 interposed therebetween. Further, an electric field relaxation layer 130 made of n-type GaN is formed between the two gate electrodes 114 and the channel portion 140 and the channel portion 141 formed below the gate electrode 115, respectively. Here, the two gate electrodes 114, the gate electrode 115, the insulating film 116, and the electric field relaxation layer 130 are formed substantially symmetrically with respect to the center line between the ohmic electrode 110 and the ohmic electrode 112.

  In this bidirectional switching 20, normally-off operation and bidirectional switching are possible as in the first embodiment, and the on-resistance can be reduced because the two gate electrodes 114 and 115 are provided. .

Furthermore, since the two gate electrodes 114 and 115 can be controlled independently, switching characteristics such as high-speed response are further improved by controlling the voltage appropriately in a bidirectional switching operation. be able to.
In addition, since the distance between the gate electrode 114 and the ohmic electrode 112 and between the gate electrode 115 and the ohmic electrode 110 can be increased with the same element area, the reverse breakdown voltage is increased as compared with the case where there is one gate electrode. be able to.

(Embodiment 3)
FIG. 4 is a schematic cross-sectional view showing a bidirectional switching element according to Embodiment 3 of the present invention. In addition to the configuration of the bidirectional switching element 20, the bidirectional switching element 22 includes an electric field relaxation layer 131 made of n-type GaN between the channel part 140 and the contact layer 120 and between the channel part 141 and the contact layer 122. Each has.

  In this bidirectional switching element 22, normally-off operation and bidirectional switching are possible as in the second embodiment, and an electric field is provided between the gate electrode 114, the gate electrode 115, the ohmic electrode 110, and the ohmic electrode 112. Since the relaxation layer 131 is provided, the electric field concentration can be further relaxed and the withstand voltage characteristic is further improved.

(Embodiment 4)
FIG. 5 is a schematic cross-sectional view of a bidirectional switching element according to Embodiment 4 of the present invention.
In this bidirectional switching element 30, a buffer layer 102, a lower semiconductor layer 203 made of p-type GaN, an operation layer 204 made of undoped GaN or n-type GaN, and an electron supply layer 206 made of AlGaN are sequentially stacked on a substrate 100. ing. On the electron supply layer 206, two ohmic electrodes 110 and an ohmic electrode 112 are formed at a predetermined interval, and the electron supply layer 206 is disposed at a predetermined position between the two ohmic electrodes 110 and the ohmic electrode 112. A first gate electrode 215 that is in Schottky contact is formed. Furthermore, an opening 150 that penetrates the electron supply layer 206 and reaches the electron transit layer 204 is provided at another position between the two ohmic electrodes 110 and 112, and the opening 150 has an insulating property. A second gate electrode 214 is formed through the film 216.

  A two-dimensional electron gas (2DEG) layer due to the piezoelectric effect is generated at the heterojunction between the electron transit layer 204 made of GaN and the electron supply layer 206 made of AlGaN. Since the 2DEG layer has high conductivity and carrier mobility, the bidirectional switching element 30 can suppress a decrease in channel mobility, and the gate electrode 214 is formed through the insulating film 216. Therefore, gate leakage can be reduced.

It is a cross-sectional schematic diagram of the bidirectional | two-way switching element which concerns on Embodiment 1 of this invention. It is a cross-sectional schematic diagram which shows the manufacturing process of the bidirectional | two-way switching element which concerns on Embodiment 1 of this invention. It is a cross-sectional schematic diagram of the bidirectional | two-way switching element which concerns on Embodiment 2 of this invention. It is a cross-sectional schematic diagram of the bidirectional | two-way switching element which concerns on Embodiment 3 of this invention. It is a cross-sectional schematic diagram of the bidirectional | two-way switching element which concerns on Embodiment 4 of this invention. It is a circuit diagram which comprises the conventional bidirectional | two-way switching element.

Explanation of symbols

10, 20, 22, 30 Bidirectional switching element
100 Substrate 102 Buffer layer 104 Operation layer 110, 112 Ohmic electrode 114, 115, 214, 215 Gate electrode 116, 216 Insulating film 120, 122 Contact layer 130-132 Electric field relaxation layer 140-144 Channel 150 Opening 203 Lower semiconductor layer 204 Electron travel layer 206 Electron supply layer

Claims (6)

A switching element made of a GaN compound semiconductor,
An operating layer having one conductivity type;
A first electrode and a second electrode formed on the operating layer so as to be separated from each other;
A first contact layer having an opposite conductivity type in the working layer and formed in contact with the first electrode;
A second contact layer having an opposite conductivity type in the working layer and formed in contact with the second electrode;
On the operating layer, at least one gate electrode formed substantially symmetrically with respect to the center line between the first electrode and the second electrode via an insulating film;
A channel portion formed in a portion of the operation layer corresponding to the gate electrode;
And at least one electric field relaxation layer formed between the first electrode and the second electrode and having an opposite conductivity type having an impurity concentration lower than that of the first contact layer and the second contact layer. Bi-directional switching element. One gate electrode is formed between the first electrode and the second electrode,
2. The bidirectional device according to claim 1, wherein the electric field relaxation layer is formed between the first contact layer and the channel portion and between the second contact layer and the channel portion. Switching element. Two gate electrodes are formed between the first electrode and the second electrode,
The bidirectional switching element according to claim 1, wherein the electric field relaxation layer is formed between two channel portions formed in a portion corresponding to the two gate electrodes. The GaN-based compound semiconductor is Al _x In _y Ga _1-xy N (where 0 ≦ x <1, 0 ≦ y <1, 0 ≦ x + y ≦ 1). The bidirectional switching element according to claim 3. a p-type semiconductor layer;
An operation layer stacked on the p-type semiconductor layer;
An electron supply layer made of a semiconductor material stacked on the operation layer and having a wider band gap than the operation layer;
A first ohmic electrode and a second ohmic electrode formed on the electron supply layer;
A first gate electrode formed on the electron supply layer between the first ohmic electrode and the second ohmic electrode;
The second ohmic electrode provided between the first ohmic electrode and the second ohmic electrode is provided through an insulating film in an opening reaching the electron transit layer formed at a predetermined position of the operation layer. A bidirectional switching element comprising a gate electrode. The p-type semiconductor layer is a p-type GaN layer;
The operating layer is an undoped GaN or n-type GaN layer,
6. The electron supply layer according to claim 5, wherein the electron supply layer is an Al _x In _y Ga _1-xy N (where 0 <x <1, 0 ≦ y <1, 0 ≦ x + y ≦ 1) layer. The bidirectional switching element as described.

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