JP5713431B2 - Field effect transistor - Google Patents

Description

  The present invention relates to a field effect transistor, and more particularly to a field effect transistor including a diamond thin film layer.

  Diamond semiconductors not only have the maximum dielectric strength and thermal conductivity of semiconductors, but also have high electron and hole mobility and drift speed, and if they are field effect transistors using diamond thin films (hereinafter referred to as “diamond FETs”). If it can be put into practical use, a high-frequency power transistor with the highest performance that far exceeds the performance of existing semiconductors can be put into practical use.

  With reference to FIG. 2, a conventional process for producing a hydrogen-terminated diamond FET will be described.

  First, a diamond crystal layer 201 is prepared, the crystal layer 201 is exposed to hydrogen plasma in a CVD reactor, and the diamond surface is terminated with hydrogen radicals (represented by “H”) (FIG. 2A). A hydrogen-terminated surface layer 202 is thus formed. Next, two gold thin films 203A and 203B spatially separated are vapor-deposited in a partial region on the surface layer 202 (FIG. 2B). These become the source electrode 203A and the drain electrode 203B, respectively. Next, an Al thin film 204 is deposited by spatial separation between the source electrode 203A and the drain electrode 203B. This becomes the gate electrode 204 (FIG. 2C). FIG. 2D shows the wiring for operating the FET manufactured as described above.

  FIG. 3 shows the drain current characteristics of an FET having a gate length of 1 μm manufactured by such a conventional technique. The maximum drain current density at a gate voltage of −3 V of the FET according to the prior art was 100 mA / mm at 30 ° C. Furthermore, as shown in FIG. 3, when the sample temperature was raised, the drain current density decreased rapidly around 150 ° C., and the drain current density did not return to room temperature even when the temperature was returned to room temperature (Non-Patent Document). 1).

M. Kubovic, Y. Yamauchi, M. Kasu, “Improvements in Thermal Stability of Hydrogen-terminated Diamond FETs”, Extended Abstract of the 2008 International Conference on Solid State Devices and Materials, Tsukuba, 2008, pp. 1036-1037.

  In the above-described diamond FET according to the prior art, (1) the maximum drain current density at room temperature is low, and (2) when the temperature of the sample is raised, the drain current is dramatically reduced and deteriorated at a certain temperature or higher. Is a problem and cannot be put to practical use.

  The present invention has been made in view of such problems, and an object thereof is to improve drain current characteristics in a diamond FET. Another object of the present invention is to provide a diamond thin film that can be used for such FETs.

In order to achieve such an object, according to the first aspect of the present invention, the boron concentration is 2 × 10 ²⁰ cm ⁻³ or more and 3 × 10 ²¹ cm ⁻³ or less, and the film thickness is 1 nm or more and 5 nm or less. It is a diamond thin film characterized by this.

  A second aspect of the present invention includes a diamond crystal layer, a channel layer on the diamond crystal layer, and a source electrode, a drain electrode, and a gate electrode on the channel layer, and the channel layer includes a first layer It is comprised with the diamond thin film of the aspect.

  According to a third aspect of the present invention, in the second aspect, a TiC layer is provided between the source and drain electrodes and the channel layer.

According to a fourth aspect of the present invention, in the second or third aspect, an Al ₂ O ₃ layer is provided between the gate electrode and the channel layer.

According to the present invention, a diamond thin film characterized in that the boron concentration is 2 × 10 ²⁰ cm ⁻³ or more and 3 × 10 ²¹ cm ⁻³ or less and the film thickness is 1 nm or more and 5 nm or less is used for the channel layer. Thus, the drain current characteristics can be greatly improved in the diamond FET.

It is a figure for demonstrating the manufacturing process of the diamond FET by this invention. It is a figure for demonstrating the manufacturing process of the conventional hydrogen-terminated diamond FET. It is a figure which shows the drain current voltage characteristic of the diamond FET by a prior art and this invention. It is a figure which shows the film thickness dependence of the sheet carrier density | concentration of a high concentration boron dope diamond thin film layer. It is a figure which shows the sheet | seat hole density | concentration with respect to the boron atom density | concentration of a high concentration boron dope diamond thin film layer. It is a figure which shows the temperature dependence of the diamond thin film layer concerning this invention. In the case of (a) corresponding to the prior art having only the Au layer without the TiC layer and the Ti layer, and in the case of the present invention having the TiC layer and the Ti layer in addition to the Au layer ((b)) It is a figure which shows the current voltage characteristic between drain electrodes.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Although description will be made with reference to specific materials and numerical values, the scope of the present invention is not intended to be limited to these materials and numerical values.

  The structure of the diamond FET according to the present invention will be described along the manufacturing process.

  First, a raw material gas obtained by diluting trimethylboron (TMB) and methane with hydrogen is supplied on the surface of the diamond crystal layer 1 with a microwave CVD apparatus to grow a diamond thin film layer 102 doped with boron at a high concentration. (FIG. 1 (a)). The microwave power during crystal growth was 500 W, the substrate temperature was 600 ° C., and the B / C atomic concentration ratio was 6000 ppm.

  Next, Ti layers 131A and 131B and Au layers 132A and 132B are sequentially deposited as a source electrode and a drain electrode (FIG. 1B).

Next, the sample is annealed at 400 ° C., and Ti is reacted with diamond to form TiC layers 133A and 133B (FIG. 1C). Finally, an Al ₂ O ₃ film 141 is formed in a gate portion spatially separated from the source electrode and the drain electrode, and an Al layer 42 is deposited thereon as a gate electrode (FIG. 1D). FIG. 1 (e) shows the wiring for operating the diamond FET thus manufactured.

  FIG. 3 shows the drain current characteristics of the fabricated diamond FET. The characteristics of the FET according to the present invention were 600 mA / mm at the maximum drain current density at a gate voltage of −3 V, which was about 6 times that of the conventional technique. Regarding the temperature dependency, the drain current density rapidly decreased from room temperature to around 150 ° C. in the prior art, but in the present invention, it stably operated up to 900 ° C.

FIG. 4 shows the sheet carrier concentration when the thickness of the diamond thin film layer 102 is changed. When the film thickness was in the range of 1 to 5 nm, the sheet carrier concentration was 1 × 10 ¹⁴ cm ⁻² or more, and it was found that good characteristics were exhibited. FIG. 5 shows the sheet hole concentration with respect to the boron atom concentration. When 2 × 10 ²⁰ to 3 × 10 ²¹ cm ⁻³ , the sheet hole concentration was 1 × 10 ¹⁴ cm ⁻² or more, which was found to be favorable. FIG. 6 shows the temperature dependence of the diamond thin film layer. In the prior art, the sheet hole concentration rapidly decreases as the temperature rises, but in the present invention, it is stable at approximately 1 × 10 ¹⁴ cm ⁻² .

As described above, a diamond thin film having a boron concentration of 2 × 10 ²⁰ cm ⁻³ or more and 3 × 10 ²¹ cm ⁻³ or less and a film thickness of 1 nm or more and 5 nm or less has a sheet carrier concentration and mobility. Take good value. By using such a diamond thin film as the channel layer of the FET, as described with reference to FIG. 3, the drain current characteristic is greatly improved. Since the maximum drain current density is greatly increased and the temperature characteristics are stabilized, a practically usable diamond FET can be manufactured.

  FIG. 7 shows a case in which the TiC layers 133A and 133B and the Ti layers 131A and 131B are not present and only the Au layers 132A and 132B correspond to the prior art ((a)), and the TiC layer 133A in addition to the Au layers 132A and 132B. 1B shows current-voltage characteristics between the source and drain electrodes in the case of the present invention having 133B and Ti layers 131A and 131B ((b)). It was found that the current value was clearly higher in the case of the present invention and the resistance was lower.

101 diamond crystal layer 102 diamond thin film layer 131A, 131B Ti layer 132A, 132B Au layer 133A, 133B TiC layer 141 Al ₂ O ₃ film 142 Al layer

Claims (2)

A diamond crystal layer;
A channel layer on the diamond crystal layer;
A source electrode, a drain electrode and a gate electrode on the channel layer;
The channel layer is composed of a diamond thin film having a boron concentration of 2 × 10 ²⁰ cm ^{−3 to} 3 × 10 ²¹ cm ⁻³ and a film thickness of 1 nm to 5 nm .
A field effect transistor comprising an Al ₂ O ₃ layer between the gate electrode and the channel layer . The field effect transistor according to claim 1 , further comprising a TiC layer between the source electrode, the drain electrode, and the channel layer.

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