Advantages
- Significantly Lower Process Temperatures: Capable of film deposition through heat treatment below 500°C, enabling damage-free direct deposition onto glass, plastics, and existing LSI chips.
- Overwhelmingly High Mobility Compared to Conventional Methods: Achieving a large grain size of approximately 5 μm through a proprietary temperature-control process, yielding a hole mobility (up to 380 cm^2/Vs) that surpasses conventional germanium (Ge) on glass. Furthermore, metal-assisted grain boundary control technology recorded an overwhelmingly high mobility of up to 690 cm^2/Vs.
- World's First Demonstrated Flexible Ge-CMOS Operation: Successfully forming p/n-channel TFTs on plastic and demonstrating the operation of CMOS logic circuits.
Background and Technology
To realize next-generation flexible information terminals such as foldable smartphones and smart glasses, logic circuits must be directly implemented on sheet-like substrates like plastics. Germanium (Ge), which enables advanced and high-speed information processing, is highly anticipated as an alternative to silicon, which suffers from low carrier mobility. A research group led by Professor Kaoru Toko at the University of Tsukuba, aims to develop TFTs (thin-film transistors) using Ge, which features high mobility and a relatively low crystallization temperature.
Professor Toko's research has made significant breakthroughs. By developing a proprietary low-temperature solid-phase crystallization process that precisely controls temperature during film deposition, the group successfully formed ultra-high-quality polycrystalline Ge thin films with giant crystal grains (approx. 5 μm) at low temperatures (from 375°C) that plastic substrates can withstand. This solves the conventional challenge where forming Ge films on low-heat-resistant plastics (with an upper limit of approx. 400°C) introduces grain boundaries and defects, severely degrading mobility.
Furthermore, by forming p/n-channel TFTs on plastic, they achieved the world's first stable operation of a flexible Ge-CMOS logic circuit on a plastic film. Previously, it was considered difficult to form adjacent p-channel and n-channel transistors on the same substrate—a requirement for logic circuits—but this technology has overcome that hurdle.
This technology is expected to be widely utilized not only for CMOS in next-generation flexible information terminals (foldable smartphones, smart glasses, etc.) but also for near-infrared sensors, transparent displays, as well as the memory and CPUs embedded within them.
For more details, please watch the report video : https://youtu.be/dquX5ABunEk (Please use translation function in Youtube)
Current Stage and Key Data
**Current Stage**
- Successfully developed ultra-high-quality polycrystalline p/n-channel Ge-TFTs on plastic films, achieving record-breaking electron and hole mobilities.
- Demonstrated the world's first operation of a polycrystalline Ge-CMOS logic circuit (inverter).
**Next Steps**
Further performance enhancement and verification towards the commercialization of flexible Ge-based CMOS.
**Key Data**
- By depositing amorphous Ge on a glass substrate at a substrate temperature of 125°C and applying heat treatment at 375–450°C, the crystal grain size was enlarged to approximately 5 μm, achieving a hole mobility of 340 cm2/Vs (380 cm2/Vs at a thickness of 300 nm).
- In evaluations combining grain boundary control via metal addition, a dramatic quality improvement was achieved, reaching a hole mobility of 690 cm2/Vs.
- A polycrystalline Ge-CMOS inverter circuit was fabricated using this technology on a heat-resistant polyimide film, confirming stable inverting amplification operation in a flexible environment for the first time in the world.
Partnaring Model
The University of Tsukuba is seeking joint development opportunities with semiconductor development companies exploring next-generation devices to commercialize flexible Ge-based CMOS. Meetings with the inventors can be arranged, so please feel free to contact us.
Principal Investigator
Kaoru Toko, PhD (Professor, University of Tsukuba, Japan)
Patents and Publications
- Patents: Patented in Japan (Patent No. 6985711)
- Moto K et al., Adv. Electron. Mater. 11, 2400901 (2025). https://doi.org/10.1002/aelm.202400901
- Toko K et al., Appl. Phys. Rev. 12, 031318 (2025).