H. Sunamura

Highly reliable BEOL-transistor with oxygen-controlled InGaZnO and Gate/Drain offset design for high/low voltage bridging I/O operations

Reliability of BEOL-transistors with a wide-gap oxide semiconductor InGaZnO (IGZO) film, integrated on LSI Cu-interconnects, is intensively discussed in terms of application to on-chip bridging I/Os between low and high voltage interactive operations (Fig. 1). Oxygen control in the thin IGZO film was found to be important to stabilize the device characteristics. A conventional IGZO tends to contain deep-level donor-states, which cause temperature and bias instabilities. The oxygen control in IGZO reduces these deep donor-states to improve operation instability. A gate/drain offset structure effectively suppresses the hot-carrier generation, resulting in a stable operation at high Vd bias condition (∼20V). The oxygen-controlled IGZO and gate/drain offset structure are important for making the BEOL-transistors applicable to high/low voltage I/Os bridging.

Operation of functional circuit elements using BEOL-transistor with InGaZnO channel for on-chip high/low voltage bridging I/Os and high-current switches

Functional circuit elements based on novel BEOL-transistors with a wide-band-gap oxide semiconductor InGaZnO (IGZO) film are integrated onto LSI Cu-interconnects, and their operations are demonstrated. High-current comb-type transistors show excellent Ion/Ioff ratio (>;108) and high-Vd operation with linear area dependence, realizing area-saving compact high-current BEOL switches. Successful operation of voltage-controlled inverter switches with high-Vd enables on-chip bridging I/Os between high/low voltage on conventional Si system LSIs. Setting the gate-to-drain offset design to just 0.1μm realizes +20V enhancement of the breakdown voltage to ~60V with excellent safety operation at around Vd=50V due to the wide-band-gap characteristics.

High on/off-ratio P-type oxide-based transistors integrated onto Cu-interconnects for on-chip high/low voltage-bridging BEOL-CMOS I/Os

A new P-type amorphous SnO thin-film transistor with high I_on/I_off ratio of >10⁴ is developed, for the first time, as a component to complement N-type IGZO transistors for on-chip voltage-bridging BEOL-CMOS I/Os on conventional Si-LSI Cu-interconnects (Fig. 1). Dedicated low-temperature (<;400°C) oxide-semiconductor processes are implemented to overcome several integration challenges (Fig. 2) with only one-mask addition using standard BEOL process tools (Fig. 3). We demonstrate high I_on/I_off ratio of >10⁴ and high-V_d capability (|V_bd|>40V) with gate-to-drain offset structure, showing superior properties over the previously reported values (Table 1). The SnO transistor is suited for the BEOL-CMOS I/O, which gives standard LSIs a special add-on function to control high voltage signals directly in smart society applications.

Enhanced drivability of high-V bd dual-oxide-based complementary BEOL-FETs for compact on-chip pre-driver applications

Enhanced current drivability of BEOL-process-compatible dual-oxide complementary BEOL-FETs on LSI-interconnects (Fig. 1) with just two additional masks to the state-of-the-art BEOL process is demonstrated, aiming at high-Vbd pre-driver operation. We have developed processes so that IGZO-based NFETs have lower ARon as compared to currently available Si power devices (Fig. 6). We also developed new SnO processes, realizing a 30× Ion boost for PFETs. Dual oxide semiconductor channels are integrated to form BEOL-CMOS inverters with stable and sharp cut-off characteristics (Figs. 8 and 9) for lower power operation, leading to a successful operation of an integrated 6T-SRAM cell (Fig. 11). Pre-driver capability of NFET inverters is demonstrated with MCU-controlled operation of brushless DC (BLDC) motors (Fig. 12). This technology is a strong candidate to realize high-Vbd pre-drivers and low-power logic on BEOL, which gives standard LSIs a special add-on function for smart society applications.