Alexander Kalnitsky

Transistor characteristics with Ta/sub 2/O/sub 5/ gate dielectric

As the gate oxide thickness decreases below 2 nm, the gate leakage current increases dramatically due to direct tunneling current. This large gate leakage current will be an obstacle to reducing gate oxide thickness for the high speed operation of future devices. A MOS transistor with Ta/sub 2/O/sub 5/ gate dielectric is fabricated and characterized as a possible replacement for MOS transistors with ultra-thin gate silicon dioxide. Mobility, I/sub d/-V/sub d/, I/sub d/-V/sub g/, gate leakage current, and capacitance-voltage (C-V) characteristics of Ta/sub 2/O/sub 5/ transistors are evaluated and compared with SiO/sub 2/ transistors. The gate leakage current is three to five orders smaller for Ta/sub 2/O/sub 5/ transistors than SiO/sub 2/ transistors.

Leakage current comparison between ultra-thin Ta 2 O 5 films and conventional gate dielectrics

Capacitors with ultra-thin (6.0-12.0 nm) CVD Ta/sub 2/O/sub 5/ film were fabricated on lightly doped Si substrates and their leakage current (I/sub g/-V/sub g/) and capacitance (C-V) characteristics were studied. For the first time, samples with stack equivalent oxide thickness around 2.0 nm were compared with ultra-thin silicon dioxide and silicon oxynitride. The Ta/sub 2/O/sub 5/ samples showed remarkably lower leakage current, which not only verified the advantages of ultra-thin Ta/sub 2/O/sub 5/ as dielectrics for high density DRAMs, but also suggested the possibility of its application as the gate dielectric material in MOSFETs.

SiON/Ta/sub 2/O/sub 5//TiN gate-stack transistor with 1.8 nm equivalent SiO/sub 2/ thickness

SiON/Ta/sub 2/O/sub 5/ stacked gate dielectric exhibits 3-5 orders smaller leakage current than SiO/sub 2/ at 1.8 nm, while the transistor characteristics such as mobility, I/sub d/-V/sub g/, and I/sub d/-V/sub d/, are similar to those of SiO/sub 2/ transistor. N-channel MOSFET with equivalent SiO/sub 2/ thickness down to 1.8 nm (1.4 nm equivalent due to elimination of poly-Si depletion) is demonstrated. Process effects are also studied for optimum process condition.

Proton-ELISA: Electrochemical immunoassay on a dual-gated ISFET array

Here we report an electrochemical immunoassay platform called Proton-ELISA (H-ELISA) for the detection of bioanalytes. H-ELISA uniquely utilizes protons as an immunoassay detection medium, generated by the enzyme glucose oxidase (GOx) coupled with Fentons reagent in a proton amplification reaction cascade that results in a highly amplified signal. A proton-sensitive dual-gated ion-sensitive field effect transistor (DG-ISFET) sensor was also developed for sensitive and accurate detection of the proton signal in H-ELISA. The DG-ISFET sensor comprises of a 128 × 128 array of 16,384 sensing transistors each with an individually addressable back gate to allow for a very high signal throughput and improved accuracy. We then demonstrated that the platform could detect C-reactive protein and immunoglobulin E down to concentrations of 12.5 and 125 pg/mL, respectively. We further showed that the platform is compatible with complex biological sample conditions such as human serum, suggesting that the platform is sufficiently robust for potential diagnostic applications.