Abstract :
MOSFET oxide scaling for DRAM (dynamic random-access memory) applications can be limited by gate-induced diode leakage, which has been shown previously by experiments at cryogenic temperatures to consist of a thermal volume generation and a band-to-band tunneling mechanism. Tunneling is the dominant mechanism at relatively higher voltages and cryogenic temperatures. The authors have studied the leakage as a function of low applied bias and made low-temperature measurements (25 K to 400 K) of this mechanism, using a submicrometer N + polysilicon gate CMOS process. They have also studied the tunnel current dependence on gate-to-drain bias, dielectric thickness, gate-to-drain overlap, flatband voltage and bandgap narrowing for n- and p-channel devices. Experimentally the leakage current characteristic satisfies an exp(-B/Es) relationship, where Es is the electric field at the silicon dioxide-silicon interface. The coefficient B contains the tunneling temperature dependence. The leakage current has strong oxide-thickness, flatband, and voltage dependencies. By withdrawing the diffusion edge, thereby reducing the overlap area, the tunnel current decreases and has a gate voltage dependency. The gated-diode leakage impact on MOSFET dielectric scaling can be reduced by scaling gate-to-diffusion overlap
Keywords :
insulated gate field effect transistors; leakage currents; semiconductor device testing; tunnelling; 25 to 400 K; DRAM; MOSFET oxide scaling; SiO2-Si interface; band-to-band tunneling; bandgap narrowing; cryogenic temperatures; dielectric thickness; flatband voltage; gate-to-drain bias; gate-to-drain overlap; leakage current characteristic; submicrometer N+ polysilicon gate CMOS process; thermal generation gate-induced drain leakage; thermal volume generation; CMOS process; Cryogenics; Dielectric measurements; Diodes; Dynamic voltage scaling; Leakage current; MOSFET circuits; Random access memory; Temperature; Tunneling;