Rongyan Chuai

Modelling of the nanoscale channel length effect on the subthreshold characteristics of junctionless field-effect transistors with a symmetric double-gate structure

An analytical subthreshold current of deep nanoscale short channel junctionless field-effect transistors (JL FETs) with a symmetric double-gate (DG) structure has been proposed. It is derived from two-dimensional Poissons equation using a variable separation technique. The proposed models can exactly describe the behaviour of subthreshold I–V characteristics with nanoscale channel length without any empirical fitting parameter. The model accounts for channel length, body thickness, gate oxide thickness and body doping concentrations. The models are verified by comparison with TCAD simulations and show good agreement.

The Optimal Design of Junctionless Transistors with Double-Gate Structure for reducing the Effect of Band-to-Band Tunneling

The effect of band-to-band tunneling (BTBT) leads to an obvious increase of the leakage current of junctionless (JL) transistors in the OFF state. In this paper, we propose an effective method to decline the influence of BTBT with the example of ntype double gate (DG) JL metal-oxide-semiconductor field-effect transistors (MOSFETs). The leakage current is restrained by changing the geometrical shape and the physical dimension of the gate of the device. The optimal design of the JL MOSFET is indicated for reducing the effect of BTBT through simulation and analysis.

A continuous current model of ultra-thin cylindrical surrounding-gate inversion-mode Si nanowire nMOSFETs considering a wide range of body doping concentration

Based on the approximated solution of Poissons equation, we propose a continuous current model of ultra-thin fully depleted cylindrical surrounding-gate Si nanowire MOSFETs. It matches well with three-dimensional simulation results using SILVACO Atlas TCAD in a wide range (from intrinsic to high doping) of the body doping concentration without any empirical fitting parameters. It is valid for all the operation regions such as subthreshold, turn-on, linear and saturation.

Piezoresistive properties of heavily doped P-type polysilicon films

The different thickness polysilicon films were prepared by low pressure chemical vapor deposition. The microstructures of samples were observed by X-ray diffraction, scanning electron microscope and transmission electron microscope. The piezoresistive properties of samples were tested. The experimental results show that under high doping concentration, the gauge factor of polysilicon nanofilms is larger than that of common polysilicon films, which can not be explained reasonably by existing piezoresistive theories, but can be well explained by tunneling piezoresistive theory. The experimental results imply that the polysilicon nanofilms is a promising high temperature piezoresistive material.

Self-testable Pressure Sensors Based on Phase Change

Novel self-testable pressure sensors based on phase change have been fabricated. The sensors were built in a glass-silicon-glass sandwich structure. Water acted as the phase change material (PCM) was injected into the cavity of the pressure sensor. Applying voltage to the heating resistor, the PCM boiled. The vapor produced by phase change can produce high enough self-testable output. Therefore, the method had been used for large-scale pressure sensors. The design and simulation of the new structure, the main fabrication process, and the experimental results on the self-testable function were presented. The self-testable output is up to 3.0% of the full-scale output

Design, Preparation and Performance Study of On-Chip Flow-Through Amperometric Sensors with an Integrated Ag/AgCl Reference Electrode

To improve the reference potential stability of on-chip amperometric sensors, we propose a novel integrated Ag/AgCl reference electrode structure. This structure can refresh the saturated potassium chloride filling solution surrounding the Ag/AgCl electrode. We then designed a flow-through amperometric sensor and a multilayer microfluidic chip based on the integrated reference electrode. In order to improve the detection signal strength of the flow-through sensor, a numerical simulation model was established. The simulation results showed that a combination of (1) using a step-type detection cell structure that maintains micro-channel width while reducing micro-channel height, and (2) controlling the sample flow rate to limit the mass transfer of the sensor surface effectively, improves the detection signal strength. The step-type detection cell structure had dimensions of 200 μm × 200 μm × 100 μm (length × width × height), and the electroosmotic flow driving voltage was 120 V/cm. Finally, successful trace detection of Mg2+ and Pb2+ in the water was achieved using the amperometric sensor and microfluidic chip: detection limits were 5 μmol/L and 84 μmol/L. The preparation of an on-chip flow-through amperometric sensor with an integrated Ag/AgCl reference electrode will facilitate improved portability of microfluidic detection technology.

The algorithm for the piezoresistance coefficients of p-type polysilicon*

In order to improve the piezoresistance theory of polysilicon, based on the tunneling piezoresistance model, using the mechanisms of approximate valence band equation and shifts of the hole transfer and hole conduction mass by stress, a novel algorithm for the piezoresistance coefficients of p-type polysilicon is presented. It proposes three fundamental piezoresistance coefficients π11, π12 and π44 of the grain neutral and grain boundary regions, separately. With those piezoresistance coefficients, the gauge factors of the p-type polysilicon nanofilm and the p-type common polysilicon film are calculated, and then the plots of the gauge factor as a function of doping concentration are given, which are consistent with the experimental results.

DC electrical trimming characteristics of polysilicon nanofilms with different doping concentrations

Polysilicon nanofilms (less than 100nm in thickness) have been proved in our previous experiments to offer large gauge factor (≫30) and stable temperature characteristics. This promotes their applications in piezoresistive sensing devices. In order to improve the resistance matching of sensors after fabrication, it is necessary to perform resistor trimming. The electrical trimming is an effective method of correcting resistance error and mismatch. Therefore, in this paper, the electrical trimming characteristics of polysilicon nanofilm (PSNF) resistors with heavy doping concentrations were investigated. For the sample preparation, PSNFs were deposited on thermally oxidized Si substrates by LPCVD at 620°C and doped heavily at different doses by boron ion-implantation and post-annealing. The resistance changes of trimmed resistors were measured after a series of incremental DC current higher than the threshold current density is applied. Based on the as-established interstitial-vacancy (IV) model, it is considered that the phenomenon of electrical trimming is due to the recombination of IV pairs at grain boundaries under the energy excitation of Joule heat generated by high current conduction. Moreover, the occupation of implanted boron dopants to vacancies can restrain the recombination of IV pairs and influence the threshold current density. The experimental results indicate that elevating doping concentration can improve the trimming accuracy and decrease the trimming rate. It can be concluded that electrical trimming is suitable for the correction of resistance mismatch after device packaging.