Ensuring gate oxide reliability and low switching loss is required for a trench gate SiC-MOSFET. We developed a trench gate SiC-MOSFET with a p-type region, named Bottom P-Well (BPW), formed at the bottom of the trench gate for bottom oxide protection. We can see an effective reduction in the maximum bottom oxide electric field (Eox) and a significant improvement in dynamic characteristics with a grounded BPW, whose dV/dt is 76 % larger than that with a floating BPW due to reduction in gate-drain capacitance (Cgd). The grounded BPW is found to be an effective means of both suppressing Eox and reducing switching loss.
We demonstrated a marked improvement of sensitivity (signal-to-noise ratio) in carbon nanotube field-effect transistor (CNTFET) sensors. The alternating current (AC) measurement with a lock-in amplifier, which suppresses the fluctuations in drain current in CNTFETs without decreasing the signal level, was adopted. The noise level of CNTFETs used in buffer solutions was greatly decreased by AC measurement. Furthermore, we investigated the sensing operations of CNTFET pH sensors and biosensors by AC measurement. The sensing performance of CNTFET sensors was markedly improved. The signal-to-noise ratio of pH sensors measured using AC was six times higher than that obtained by direct current (DC) measurement. A small amount of bovine serum albumin of 250 pM was effectively detected by CNTFET biosensors by AC measurement. #
We have fabricated local-electrolyte-gated carbon nanotube field-effect transistors (CNTFETs), in which the electrolyte functions as a local top gate. The local-electrolyte-gated CNTFETs in the electrolyte solution provided high performance in terms of subthreshold slope and transconductance, resulting from the modulation of the conduction in the carbon nanotube channel and the large gate capacitance. Using the local-electrolyte-gated CNTFETs, real-time protein detection based on the channel conductance modulation was successfully demonstrated. Our local-electrolyte-gated CNTFETs are promising candidates for the development of nanoscale electronic and molecular-sensing device applications.
External Schottky barrier diodes (SBD) are generally used to suppress the conduction of the body diode of MOSFET. A large external SBD is required for a high voltage module because of its high specific resistance, while the forward voltage of SBD should be kept smaller than the built-in potential of the body diode. Embedding SBD into MOSFET with short cycle length increases maximum source-drain voltage where body diode remains inactive, resulting in high current density of SBD current. We propose a MOSFET structure where an SBD is embedded into each unit cell and an additional doping is applied, which allows high current density in reverse operation without any activation of body diode. The proposed MOSFET was successfully fabricated and much higher reverse current density was demonstrated compared to the external SBD. We can expect to reduce total chip size of high voltage modules using the proposed MOSFET embedding SBD.
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