研究発表

Key device/circuit technologies for realizing a 28nm-node atom switch programmable logic (AS-PL) have been developed. An advanced polymer solid-electrolyte (PSE) reduces set voltage down to 1.6 V while ensuring ON-state and OFF-state reliabilities under current and voltage stress at 125°C. A fine-grain redundancy in a cross-bar array also contributes to reduce supply voltage by 6%. A routing-based wear leveling improves programming cycles by nine times. The developed technologies allow us to design the 28nm-node AS-PL with a 32% higher performance and 11% lower power.

A fully logic-compatible, nonvolatile crossbar switch using a novel dual-layer TiOx/TaSiOy solid-electrolyte, "NanoBridge", has been developed for the first time, which is scalable to 50 nm and beyond and keeps the extremely low ON-resistance of <100 Ω A key breakthrough is the dual-layer solid-electrolyte, in which TiOx works as an oxygen absorber as well as a superior ionic conductor, thus improving the yield, ON/OFF resistance ratio (>106) and cycling endurance (>103). The highly scalable 4 × 4 crossbar switch composed of NanoBridge integrated in a local Cu interconnect of a standard CMOS is successfully configured without select transistors. The nonvolatile solid-electrolyte, crossbar switch is a promising switch element for low power and low cost reconfigurable logic. © 2009 IEEE.

A complementary atom switch (CAS) is proposed to realize low programming voltage and high off-state reliability for crossbar switch application. Two atom switches with bipolar operation are connected in series with opposite direction, in which the two atom switches work as a single element. The two off-state atom switches in the CAS complementarily divide voltage stress, greatly enlarging the off-state lifetime. The CAS is embedded in Cu BEOL on a 65-nm-node CMOS platform without degrading the CMOS and interconnect performances. The CAS using two atom switches is one of the candidates for realizing energy-efficient nonvolatile programmable switches. © 2012 IEEE.

For the first time, Cu(AlTi)-alloy active-electrode coupled with RuTa inert-electrode is proposed to improve the reliability of nonvolatile Cu atom switch. The remarkably high rupture temperature (Tr >400 oC) of the nanometer-scale Cu bridge with the high thermal resistance (Rth) is realized by the Cu-alloy without increasing programming current. The anti-Cu diffusive, RuTa-alloy improves the retention of the ON-state at 150oC and endurance to >104 cycles. The metallurgical prescription is a key to improve the reliability and switching performance of the conducting bridge. © 2012 IEEE.

Reliably of Cu damascene interconnects (DDIs) using United Hard-mask and Cap (UHC) structure, which involves the same material for both Hard-mask and Cap layers is investigated. Line-to-line insulating reliabilities such as a leakage current, TZDB and TDDB are greatly improved by using the UHC structure even without any barrier metal layers, indicating that the interline leakage path is not in a bulk of the low-k dielectric but the interface between the Cap and the CMP-damaged Hard-mask. This new Cu dual damascene interconnect with UHC provides the interconnect reliability of future ULSIs with ultra-thin barrier metals toward a barrier-metal-free structure.

A solid-electrolyte switch ("NanoBridge") has been successfully embedded into a 0.13-μm-node dual-damascene Cu interconnect using a highly reliable bilayer solidelectrolyte (TaSiO/Ta2O5) and a thin oxidation barrier, resulting in an excellent ON/OFF ratio (< 109) at a low ON resistance of 50Ω. The newly developed bilayer solid-electrolyte has improved the thermal stability during the BEOL process as well as improved electrical breakdown. The CMOS compatible NanoBridge is a promising switch to achieve high-performance and low-cost programmable LSIs.

A porous SiOCH film with k=2.3 is developed by a new concept PECVD, in which pore-involved molecules are piled up together to deposit a "molecular-pore stacked, SiOCH (MPS)" film. The pore size and the density of the film are controlled by designing the pore size and the steric-hindrance side-chains of the source molecules. A newly synthesized, 6-member ring-type, organo-siloxane with the side-chains of large steric-hindrance hydrocarbons realizes the MPS film with k=2.3. The basic feasibility of the MPS film is confirmed through the integration into Cu damascene interconnects. The MPS film is a strong candidate for the low-k, inter-metal-dielectrics in 45nm-node, ASICs.

Infrared sensor system is a major concern for inter-planetary missions that investigate the nature and the formation processes of planets and asteroids. The infrared sensor system requires signal preprocessing functions that compensate for the intensity of infrared image sensors to get high quality data and high compression ratio through the limited capacity of transmission channels towards ground stations. For those implementations, combinations of Field Programmable Gate Arrays (FPGAs) and microprocessors are employed by AKATSUKI, the Venus Climate Orbiter, and HAYABUSA2, the asteroid probe. On the other hand, much smaller size and lower power consumption are demanded for future missions to accommodate more sensors. To fulfill this future demand, we developed a novel processor architecture which consists of reconfigurable cluster cores and programmable-logic cells with complementary atom switches. The complementary atom switches enable hardware programming without configuration memories, and thus soft-error on logic circuit connection is completely eliminated. This is a noteworthy advantage for space applications which cannot be found in conventional re-writable FPGAs. Almost one-tenth of lower power consumption is expected compared to conventional re-writable FPGAs because of the elimination of configuration memories. The proposed processor architecture can be reconfigured by behavioral synthesis with higher level language specification. Consequently, compensation functions are implemented in a single chip without accommodating program memories, which is accompanied with conventional microprocessors, while maintaining the comparable performance. This enables us to embed a processor element on each infrared signal detector output channel.

A novel polymer solid-electrolyte (PSE) switch, NanoBridge, featuring forming-free programming and an extremely high OFF/ON resistance ratio of 105 has been embedded in a 90nm-node CMOS by a fully logic-compatible process. Fast programming of 10nsec is also achieved in a 50nmφ 1k-bit-cell array by introducing the PSE, enabling a short and parallel programming. The OFF-state T50 lifetime at 125°C is extrapolated to be more than 10 years. The developed switch is a strong candidate for realizing a low-power and low-cost nonvolatile programmable logic (NPL). ©2010 IEEE.

1.5x energy-efficient and 1.4x operation-speed, nonvolatile via-switch (VS) FPGA with atom switch and a-Si/SiN/a-Si varistor is demonstrated in a 65nm-node for various basic applications. For rapid and low-cost migration from VS-FPGA to ASIC, 'hard-via' to replace VS with 'ON', named VS-copy (VSC), is newly proposed. The VSC-ASIC is fabricated by sharing all the photo masks with VS-FPGA excepting one via mask revise and three VS masks skip, realizing an exact design copy with minimum NRE cost and TAT. The VS-FPGA equipped with the VSC gives energy-efficient edge device, e.g., for up-to-date AI inference algorithms, covering a wide range of chip volume with extremely low cost.