Successful Transistor Operation Demonstration of Depletion-Mode r-GeO₂ MOSFET
Patentix Inc. successfully demonstrated the transistor operation of a depletion-mode MOSFET using rutile germanium dioxide (r-GeO₂), a promising next-generation power semiconductor material. This lays the groundwork for future highly efficient power devices.
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- 📰 Published: April 1, 2026 at 01:20
- 🔍 Collected: April 1, 2026 at 01:06
- 🤖 AI Analyzed: April 22, 2026 at 10:01 (512h 55m after Collected)
March 31, 2026
Patentix Inc. (hereinafter 'the Company') has fabricated a depletion-mode MOSFET using rutile germanium dioxide (r-GeO₂), which is attracting attention as a next-generation power semiconductor material, and successfully demonstrated its transistor operation. The MOSFET is one of the basic power devices, and this result is an important foundation for the realization of enhancement-mode MOSFETs in the future.
[Background]
Rutile germanium dioxide (r-GeO₂) has a larger bandgap (4.68 eV) than silicon carbide (SiC) and gallium nitride (GaN), and since both p-type and n-type conductivity are theoretically predicted, it is attracting attention as a next-generation semiconductor material capable of realizing high-breakdown-voltage, high-output, and high-efficiency power semiconductor devices.
The Company has previously established deposition and conductivity control technologies for n-type r-GeO₂ using Sb as a dopant, successfully achieving ohmic contacts via n+ layer deposition [1], and demonstrating the operation of Schottky barrier diodes (SBDs) via n- layer deposition [2]. Meanwhile, the early realization of a MOSFET, which is also one of the fundamental power devices, was highly anticipated.
[Prior Research]
As prior research examples of MOSFETs using r-GeO₂, FET operation has been reported by forming a GeO₂ film on an SiO₂/p+ Si substrate using sputter deposition [3]. In addition, in November '25, MOSFET operation was confirmed by implanting phosphorus ions into a single crystal of r-GeO₂ grown by the TSSG method. However, the operational demonstration of a MOSFET using a heteroepitaxial film, which is expected to offer large-area substrates and high cost-competitiveness, had not been reported until now.
[Achievements]
This time, by fully utilizing the deposition technologies established by the Company, we succeeded in demonstrating the transistor operation of a depletion-mode MOSFET that can be fabricated exclusively with n-type r-GeO₂.
Figures 1(a) and (b) show a cross-sectional schematic and an optical microscope image of the fabricated r-GeO₂ MOSFET. A current blocking layer consisting of an impurity-doped r-GeO₂ film was formed on an r-TiO₂ substrate, and an Sb-doped n-channel layer (thickness: 160 nm) and source/drain n+ layers were deposited on top via selective growth. This allowed for the fabrication of a MOSFET with element isolation structures and reduced ohmic contact resistance. SiO₂ (thickness: 75 nm) was used for the gate insulating film, and Pt/Ti was used for the electrodes. In this device structure, current can be turned off by applying a negative gate voltage, which extends the depletion layer directly under the gate insulating film and blocks the current path between the drain and source.
Figure 1: (a) Cross-sectional schematic and (b) optical microscope image of the r-GeO₂ MOSFET.
The ID-VG characteristics of the fabricated r-GeO₂ MOSFET are shown in Figure 2(a). The drain current ID changed with an on/off ratio of more than 5 orders of magnitude depending on the gate voltage VG, confirming a depletion-mode transistor operation where the drain current turns off at a negative gate voltage. In the hysteresis measurement shown in the same figure, characteristic fluctuations due to gate voltage application were suppressed to a small level, suggesting that an interface with the gate insulating film having few defects was formed even though the process conditions were not fully optimized.
Also, the ID-VD chara... (Text cuts off here)
Patentix Inc. (hereinafter 'the Company') has fabricated a depletion-mode MOSFET using rutile germanium dioxide (r-GeO₂), which is attracting attention as a next-generation power semiconductor material, and successfully demonstrated its transistor operation. The MOSFET is one of the basic power devices, and this result is an important foundation for the realization of enhancement-mode MOSFETs in the future.
[Background]
Rutile germanium dioxide (r-GeO₂) has a larger bandgap (4.68 eV) than silicon carbide (SiC) and gallium nitride (GaN), and since both p-type and n-type conductivity are theoretically predicted, it is attracting attention as a next-generation semiconductor material capable of realizing high-breakdown-voltage, high-output, and high-efficiency power semiconductor devices.
The Company has previously established deposition and conductivity control technologies for n-type r-GeO₂ using Sb as a dopant, successfully achieving ohmic contacts via n+ layer deposition [1], and demonstrating the operation of Schottky barrier diodes (SBDs) via n- layer deposition [2]. Meanwhile, the early realization of a MOSFET, which is also one of the fundamental power devices, was highly anticipated.
[Prior Research]
As prior research examples of MOSFETs using r-GeO₂, FET operation has been reported by forming a GeO₂ film on an SiO₂/p+ Si substrate using sputter deposition [3]. In addition, in November '25, MOSFET operation was confirmed by implanting phosphorus ions into a single crystal of r-GeO₂ grown by the TSSG method. However, the operational demonstration of a MOSFET using a heteroepitaxial film, which is expected to offer large-area substrates and high cost-competitiveness, had not been reported until now.
[Achievements]
This time, by fully utilizing the deposition technologies established by the Company, we succeeded in demonstrating the transistor operation of a depletion-mode MOSFET that can be fabricated exclusively with n-type r-GeO₂.
Figures 1(a) and (b) show a cross-sectional schematic and an optical microscope image of the fabricated r-GeO₂ MOSFET. A current blocking layer consisting of an impurity-doped r-GeO₂ film was formed on an r-TiO₂ substrate, and an Sb-doped n-channel layer (thickness: 160 nm) and source/drain n+ layers were deposited on top via selective growth. This allowed for the fabrication of a MOSFET with element isolation structures and reduced ohmic contact resistance. SiO₂ (thickness: 75 nm) was used for the gate insulating film, and Pt/Ti was used for the electrodes. In this device structure, current can be turned off by applying a negative gate voltage, which extends the depletion layer directly under the gate insulating film and blocks the current path between the drain and source.
Figure 1: (a) Cross-sectional schematic and (b) optical microscope image of the r-GeO₂ MOSFET.
The ID-VG characteristics of the fabricated r-GeO₂ MOSFET are shown in Figure 2(a). The drain current ID changed with an on/off ratio of more than 5 orders of magnitude depending on the gate voltage VG, confirming a depletion-mode transistor operation where the drain current turns off at a negative gate voltage. In the hysteresis measurement shown in the same figure, characteristic fluctuations due to gate voltage application were suppressed to a small level, suggesting that an interface with the gate insulating film having few defects was formed even though the process conditions were not fully optimized.
Also, the ID-VD chara... (Text cuts off here)