Thin-film 3D analog IC technology realized by Nisshinbo MD and OKI

Nisshinbo Micro Devices and Oki Electric Industry (OKI) held a new technology briefing on October 17 and announced that they have jointly succeeded in the 3D integration of analog ICs. The thin-film 3D analog IC was realized using a local shielding technology developed by Nisshinbo and the OKI's proprietary CFB technology. Mr. Keiichi Yoshioka, President of Nisshinbo, revealed the company's plan to develop new value-added products using this technology, aiming for mass production in 2026, with partnering and licensing in mind.

The developed thin-film 3D analog IC technology involves a CFB process of peeling and bonding, followed by rewiring. Initially, the function of an analog IC is completely protected on the wafer substrate, and only the functional layer (thin-film layer) of the analog IC is peeled off from the substrate. The peeled thin-film analog IC is bonded onto another analog IC to integrate thin-film analog ICs in three dimensions. Up to four layers can be stacked using the proposed technology. Because the stacked analog ICs are extremely thin, crosstalk, such as interference, occurs between the upper and lower ICs.

This problem was solved by employing the Nisshinbo's local shielding technology, which involves placing a thin metal film in the optimal location between the upper and lower ICs to provide local shielding. In the case of conventional 3D integration using TSV, in which electrical connections between semiconductor chips are perpendicular to the substrate, the thickness of the IC chip is several tens to several hundreds of micrometers. However, the thin-film analog IC bonded using the new technology is extremely thin, having a thickness of just few micrometers. It is therefore possible to rewire using conventional semiconductor lithography, and conventional, inexpensive old equipment can be used for rewiring. Unlike digital ICs, which distinguish between "0" and "1," analog ICs are characterized by the signal strength. Therefore, variations in elements, such as transistors and resistors, in the circuit have a major impact on the characteristics of the circuit. Therefore, miniaturization was possible only to a limited extent due to its effects on element variations.

The proposed technology can be utilized in semiconductor manufacturing methods using existing older-generation manufacturing technologies and equipment to increase the integration level. Furthermore, thin-film analog ICs can be used in heterogeneous integration, in which a single semiconductor device is divided into multiple small chips (chiplets) and integrated using a packaging technology or in which multiple chiplets of different types are combined into a single package.

Advances in sensing technology play an important role in today's AI, autonomous driving, and advanced driver-assistance systems (ADASs). In ADAS, for example, AI analyzes large amounts of data obtained from multiple sensors, such as cameras and millimeter-wave radar, to instantly determine vehicle movement and surrounding environment changes. The number of in-vehicle sensors used in cars has already exceeded 50. There is a need for more flexibility with respect to installation locations and miniaturization through integration. Sensors output weak analog signals that must be captured stably and accurately without noise. This increases the demand for small, high-performance analog ICs. However, attempts to miniaturize analog ICs comes at the cost of reduced breakdown voltage and increased noise. In the past, solving these problems required long-term process development and large capital investment.

Nisshinbo, which aims to be an "analog solution provider," uses analog technology at its core to comprehensively solve problems faced by semiconductor users, and has been working on the 3D integration of analog ICs to meet the demand for miniaturization. This time, by combining the analog IC technology that the company developed over many years with the OKI's proprietary CFB technology, the company realized a groundbreaking technology that enables the miniaturization of analog ICs via stacking while maintaining their performance. Moreover, as ICs can be manufactured using old facilities, no large investments are required. The analog IC market size currently exceeds 10 trillion yen. It is a growing market, with a CAGR of 7%. The market is expected to grow in all areas of consumer and industrial equipment, including in-vehicle devices such as sensors. Therefore, the demand for the developed thin-film 3D IC technology is expected to be significant.