We demonstrate high-performance Schottky CMOS transistors with NiSi source/drain and gate-all-around (GAA) silicon nanowire (∼5 nm) channels. The transistors exhibit good I on /I off characteristics, along with fully controlled shortchannel effects revealed by low drain-induced barrier lowering (∼10 mV/V) and near-ideal subthreshold swing (∼60 mV/dec). Although the N-MOSFET required dopant segregation to suppress the ambipolar behavior, excellent P-MOSFET characteristics could be achieved without the use of barrier modification techniques. We attribute this to the Schottky barrier thinning in a nanosized metal-semiconductor junction and superior gate electrostatic control in a GAA nanowire architecture.
Elastic storage has been reported to help flying insects save inertial power when flapping their wings. This motivates recent research and development of elastic storage for flapping-wing micro air vehicles (fwMAVs) and their ground (tethered) flight tests. The previous designs of spring-loaded transmissions are relatively heavy or bulky; they have not yet been adopted by freely hovering prototypes of fwMAVs, especially those with four flapping wings. It is not clear if partial elastic storage can still help save power for flapping flight while not overloading the motorized transmission. Here, we developed ultralight and compact film hinges as elastic storage for four flapping wings. This spring-assisted transmission was motor driven such that the wing beat frequency was higher than the natural frequency of elastically hinged wings. Our experiments show that spring recoil helps accelerate wing closing thus generating more thrust. When powered by a 3.18 g brushless motor, this 13.4 g fwMAV prototype with spring-assisted transmission can take off by beating four flexible wings (of 240 mm span) with up to 21–22 g thrust generation at 22–23 Hz. Due to lower disk loading and high-speed reduction, indirect drive of the four elastically hinged wings can produce a thrust per unit of electrical power of up to 4.6 g/W. This electrical-power-specific thrust is comparable to that generated by direct drive of a propeller, which was recommended by the motor (AP-03 7000kv) manufacturer.
Abstract-A comprehensive physics-based compact model for three-terminal undoped Schottky-barrier (SB) gate-all-around silicon-nanowire MOSFETs is formulated based on a quasi-2-D surface-potential solution and the Miller-Good tunneling model. The energy-band model has accounted for the screening of the gate field by the electrons or holes, which has been largely missed in the literature. Although SB-MOSFETs are essentially ambipolar devices, we show that the separate modeling of electron and hole currents is simple yet accurately predicts the final ambipolar current. Thinner oxide thickness is confirmed to be beneficial to SB-MOSFETs for both ON-and OFF-state currents. However, smaller nanowire radius (or thinner body thickness) is found to be only beneficial to SB-MOSFETs with high SB heights (SBHs) despite the OFF-state current being reduced significantly. For SB-MOSFETs with low SBHs, the tunneling-current-density enhancement due to a smaller radius is not able to compensate the reduction in the contact size, which leads to a degradation of the "ON" current. The drift current in the channel is shown to be negligible in SB-MOSFETs, and the tunneling/thermionic current through the SB represents the main current-limiting mechanism.
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