As a global leader in three-dimensional stacking (3D-IC) and chiplet integration technologies, which are driving performance improvements in next-generation semiconductors, our laboratory has spearheaded research in chip-to-wafer type three-dimensional integration for over 20 years. Utilizing unique technologies, including "self-alignment packaging" that leverages the surface tension of droplets, we have tackled the challenging trade-off between positional accuracy and throughput, contributing to the realization of ultra-high-speed, low-power AI chip systems.
Furthermore, we have developed "dilet" technology, which miniaturizes silicon chips and embeds them in flexible substrates, establishing a platform that enables high-performance device mounting on curved surfaces. This has made significant contributions to the integration and applied research of flexible devices, such as wearable systems that naturally fit the arm, blood vessel visualization sheets, and low-power phototherapy devices that integrate chips and fine wiring into hydrogels primarily composed of water.

From basic research to social implementation utilizing GINTI, we are promoting consistent technological development and opening up new possibilities in semiconductor integration technology.

Compared to conventional planar mounting, vertical stacking of chips (3D-IC) shortens wiring length and dramatically improves signal transmission capability and energy efficiency. Furthermore, self-alignment enables the simultaneous placement of tens of thousands of tiny chips at ultra-high speed and precision

• At IEDM2005, we demonstrated the world's first chip-to-wafer 3D stacking, and since then, we have continued to showcase our achievements at IEDM, leading the way in industrial applications. By using the surface tension of droplets for self-alignment, we have achieved both nano-precision and high throughput, and have established dielet technology that conforms to flexible substrates, as well as die-level 3D-ICs utilizing existing ICs. Furthermore, through collaboration with GINTI and venture companies, we are promoting high-speed prototyping and social implementation.

Applications are envisioned in areas such as HPC, edge AI, and medical devices. We anticipate collaboration with materials and equipment manufacturers to co-create new materials and processes, as well as design and fabless companies exploring innovative structures.

• Recently, many tunnel magnetoresistance devices with high magnetoresistance effect are reported. These are expected to be applied to high sensitive magnetic sensors. There are many magnetic sensors with variety of the mechanism, in order to meet the demand of the very wide range of sensing magnetic field. However, there is no magnetic sensor which has high sensitivity, easy to use, operation at room temperature and low cost. Only a magnetic sensor with tunnel magnetoresistance devices can satisfy all the demand in principle. As the device has very wide range of the sensing magnetic field, it can be designed for any demand to the sensors.

For example, this device can sense a bio-magnetic field easily at room temperature, so that it could be replaced SQUID device, which is popular now but is very expensive and not easy to use personally. Therefore, by using this device, we expect we can conduct effective collaborative research in medical field.

• Highly-sensitive NMR technique has been developed by manipulation polarization of nuclear spins via control of transport characteristics in GaAs and InSb quantum structures. This highly-sensitive NMR can be applied to two-dimensional and nanostructures. Furthermore, ideal gate controllability has been demonstrated in InSb quantum structures with Al2 O3 dielectrics. More importantly, the concept of generalized coherence time was introduced, where noise characteristics felt by nuclear spins can be measured including their frequency dependence. This concept will bring about a change in all nuclear-spin related measurements.

Next generation InSb devices based on good gate controllability. Various nuclear-spin based measurements and NMR utilizing the concept of generalized coherence time. Highly-sensitive NMR is now important for fundamental physics studies. In the future, it will contribute to quantum information processing.

• Recently, with a spread of high definition video streaming services and ubiquitous network, development of high-quality, ultra-realistic and low-power display systems has been demanded. We have been studying physical properties of liquid crystal materials, precise control technique of polarization, high performance liquid crystal display (LCD) devices and its application to the advanced display systems for the realization of new media such as electric paper display and digital signage display, and low-energy society. We established a polarization control technology which realizes a precise control of polarization with liquid crystal materials. By using this world-leading technology, we have been studying the control of the surface alignment of liquid crystal molecules and developed a wide-viewing angle and fast switching liquid crystal display, ultra-high definition field-sequential-color display (Fig. 1), ultra-low power reflective full-color display (Fig. 2) and large-size high-quality display system.
• We are also studying the ultra-realistic display systems such as a spatial 3D display and a multiple directional viewing display based on the precise light control technique as a next generation interactive communication technologies (Fig.3). We hope to conduct collaborative research with a willing company for a practical application of this technology in industry.

• A new dry-contact technique for transduction of broadband, high-frequency ultrasound via a solid layer inserted between water and the sample, whereat the pressure of about 0.1 MPa is applied at the layer/sample interface by evacuating air between them, has been developed. Based on the technique, acoustic imaging of an electronic package is realized under the dry environment (Fig. 1). Typically, the polymer films are used as the intermediate layer for water protection of the sample, and by utilizing the acoustic resonance phenomenon among water, film and the sample, higher quality acoustic image of the testing sample than that for the water immersion case can be recorded without getting the sample wet (Fig. 2). Moreover, thin materials, e.g., polymer film (Fig. 3), etc. can be characterized by analyzing the acoustic resonance phenomenon among the three media. We hope to conduct collaborative research with a willing company for a practical application of this technology in industry.

Ultrasonic measurement is an important technique that is used in various fields of science and technology, including physical property evaluation, imaging and sensing. I use a measurement technique that uses light to excite and detect ultrasonic waves in the frequency range of GHz to THz, and I use this to evaluate the mechanical and acoustic properties of microstructures and thin films with sizes in the nano to micro range, as well as for non-destructive testing.

Conventional ultrasound had a wavelength of several micrometres or more, so it was impossible to measure at the nanoscale.
However, by using femtosecond pulse lasers to manipulate ultrasound with a wavelength of the order of 10 nm, I have achieved the evaluation of the mechanical properties of nano-materials and non-destructive testing in the nano-region.

• Development of unique measurement technology that makes full use of light and sound (lasers and ultrasound)
• Excitation and detection of vibration phenomena in nano-materials and GHz bands
• Accurate measurement of sound velocity and elastic constants under high magnetic fields of 10 to 600 K and up to 5 T
• Measurement of magnetic damping constants and saturation magnetisation from magnetisation oscillations in the time domain
• Main targets include nano-thin films of metals, piezoelectric materials, and magnetic materials, as well as superhard materials such as diamond and tungsten carbide
• Contributing to the development of materials and the elucidation of the characteristics of filters for wireless communication in smartphones
• Applications include the development of highly sensitive biosensors using ultrasound, which has a shorter wavelength than light, and monitoring the breaking process of nanowires

This measurement method enables the inspection of defects in semiconductors on the order of nm, and the evaluation of the characteristics of acoustic filters, which are essential for 5G communication devices.

• For producing a new functionality from metallic micro and nano matarials, the welding and cutting technologies for small scale materials utilizing Joule heat has been developed (Fig. 1). A constant direct current is supplied to the system, where the free ends of two metallic wires are contacted, and the ends are successfully welded together in self-completed manner. This technology is also useful for manipulating a small scale materials.

Joule heat welding technology enables us to produce the functional elements on the electrode chips, e.g., a free-standing micro-ring and very-thin thermoelectric element (Fig. 2). Moreover, we have developed the technique for characterizing the physical properties of small scale materials (Fig. 3). We hope to conduct collaborative research with a willing company for a practical application of this technology in industry.

• Our research group has succeeded in synthesizing various metal oxide nanoparticles with controlled size and exposure crystal planes by using organic modifiers under supercritical water conditions. The oxygen storage/release capacity of those materials in the low-temperature region is very high, and the reforming reaction of oxidative hydrocarbon proceeds at a significant rate. Besides, by combining the supercritical CO2 drying method, we have succeeded in forming a complex in which oxide nanoparticles are dispersed at a high concentration on the surface of the porous material, realizing both high oxygen storage/release capability and stability.

Low-temperature reforming reaction of biomass wastes, heavy oils, and methane. In the future, it is expected to be a technology that will lead to the construction of a low-carbon society, including CO2-free complete recycling of waste plastics.