Three-to-one analog signal modulation with a single back-bias-controlled reconfigurable transistor.

Reconfigurable field effect transistors are an emerging class of electronic devices, which exploit a structure with multiple independent gates to selectively adjust the charge carrier transport. Here, we propose a new device variant, where not only p-type and n-type operation modes, but also an ambipolar mode can be selected solely by adjusting a single program voltage. It is demonstrated how the unique device reconfigurability of the new variant can be exploited for analog circuit design. The non-linearity of the ambipolar mode can be used for frequency doubling without the generation of additional harmonics. Further, phase shifter and follower circuits are enabled by the n- and p-type modes, respectively. All three functions can be combined to create a 3-to-1 reconfigurable analog signal modulation circuit on a single device enabling wireless communication schemes. Both, the concept as well as the application have been experimentally demonstrated on industrial-scale fully-depleted SOI platform. The special transport physics in those structures has been analyzed by TCAD simulations as well as temperature dependent measurements.

Channel Length-Dependent Operation of Ambipolar Schottky-Barrier Transistors on a Single Si Nanowire.

For use in flexible, printable, wearable electronics, Schottky-barrier field-effect transistors (SB-FETs) with various channel materials including low-dimensional nanomaterials have been considered so far due to their comparatively simple and cost-effective integration scheme free of junction and channel dopants. However, the electric conduction mechanism and the scaling properties underlying their performance differ significantly from those of conventional metal-oxide-semiconductor (MOS) field-effect transistors. Indeed, an understanding of channel length scaling and drain bias impact has not been elucidated sufficiently. Here, multiple ambipolar SB-FETs with different channel lengths have been fabricated on a single silicon nanowire ensuring a constant nanowire diameter. Their length scaling behavior is analyzed through drain current and transconductance contour maps, each depending on the drain and gate bias. The reduced gate control and extended drain field effect on Schottky junctions were observed in short channels. Activation energy measurements showed lower sensitive behavior of the Schottky barrier to gate bias in the short-channel device and confirmed the thinning of Schottky barrier width for electrons at the source interface with drain bias.

Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions.

Germanium is a promising material for future very large scale integration transistors, due to its superior hole mobility. However, germanium-based devices typically suffer from high reverse junction leakage due to the low band-gap energy of 0.66 eV and therefore are characterized by high static power dissipation. In this paper, we experimentally demonstrate a solution to suppress the off-state leakage in germanium nanowire Schottky barrier transistors. Thereto, a device layout with two independent gates is used to induce an additional energy barrier to the channel that blocks the undesired carrier type. In addition, the polarity of the same doping-free device can be dynamically switched between p- and n-type. The shown germanium nanowire approach is able to outperform previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents. The dielectric and Schottky barrier interface properties of the device are analyzed in detail. Finite-element drift-diffusion simulations reveal that both leakage current suppression and polarity control can also be achieved at highly scaled geometries, providing solutions for future energy-efficient systems.

Observation of higher order radial modes in atomic layer deposition reinforced rolled-up microtube ring resonators.

We present a detailed investigation of the resonator properties of high-quality rolled-up SiO2 optical microtubes reinforced by atomic layer deposition. The evolution of the resonant modes with increasing film thickness and the transition to a multimode regime, including higher order radial modes, is discussed. Measurements and simulations show that the higher order modes exhibit high optical quality and an increased extension of the evanescent field from the resonator into the surrounding matrix, making them a promising solution for future on-chip sensor applications with increased sensitivity.

Dually active silicon nanowire transistors and circuits with equal electron and hole transport.

We present novel multifunctional nanocircuits built from nanowire transistors that uniquely feature equal electron and hole conduction. Thereby, the mandatory requirement to yield energy efficient circuits with a single type of transistor is shown for the first time. Contrary to any transistor reported up to date, regardless of the technology and semiconductor materials employed, the dually active silicon nanowire channels shown here exhibit an ideal symmetry of current-voltage device characteristics for electron (n-type) and hole (p-type) conduction as evaluated in terms of comparable currents, turn-on threshold voltages, and switching slopes. The key enabler to symmetry is the selective tunability of the tunneling transmission of charge carriers as rendered by the combination of the nanometer-scale dimensions of the junctions and the application of radially compressive strain. To prove the advantage of this concept we integrated dually active transistors into cascadable and multifunctional one-dimensional circuit strings. The nanocircuits confirm energy efficient switching and can further be electrically configured to provide four different types of operation modes compared to a single one when employing conventional electronics with the same amount of transistors.

Sharp whispering-gallery modes in rolled-up vertical SiO2 microcavities with quality factors exceeding 5000.

Record high quality (Q) factors of 5400 in vertical microtube ring resonators operated in emission mode are demonstrated. This is achieved by rolling-up a differentially strained SiO2 layer. We also present a theoretical model to investigate the limit of the Q factor. This model especially includes the effect of interlayer voids in the rolled-up geometry, which is found to have a larger effect than scattering due to notches in the spiral shape.