This paper examines the performance degradation of a MOS device fabricated on silicon-on-insulator (SOI) due to the undesirable short-channel effects (SCE) as the channel length is scaled to meet the increasing demand for high-speed high-performing ULSI applications. The review assesses recent proposals to circumvent the SCE in SOI MOSFETs and a short evaluation of strengths and weaknesses specific to each attempt is presented. A new device structure called the dual-material gate (DMG) SOI MOSFET is discussed and its efficacy in suppressing SCEs such as drain-induced barrier lowering (DIBL), channel length modulation and hot-carrier effects, all of which affect the reliability of ultra-small geometry MOSFETs, is assessed.

https://web.iitd.ac.in/~mamidala/HTMLobj-161/March04.pdf

Controlling short-channel effects in deep-submicron SOI MOSFETs for improved reliability: a review

In this paper, we propose the application of a dual material gate (DMG) in a tunnel field-effect transistor (TFET) to simultaneously optimize the on-current, the off-current, and the threshold voltage and also improve the average subthreshold slope, the nature of the output characteristics, and immunity against the drain-induced barrier lowering effects. We demonstrate that, if appropriate work functions are chosen for the gate materials on the source side and the drain side, the TFET shows a significantly improved performance. We apply the technique of DMG in a strained double-gate TFET with a high-k gate dielectric to show an overall improvement in the characteristics of the device, along with achieving a good on-current and an excellent average subthreshold slope. The results show that the DMG technique can be applied to TFETs with different channel materials, channel lengths, gate-oxide materials, gate-oxide thicknesses, and power supply levels to achieve significant gains in the overall device characteristics.

Novel Attributes of a Dual Material Gate Nanoscale Tunnel Field-Effect Transistor

A two-dimensional (2-D) analytical model for the surface potential variation along the channel in fully depleted dual-material gate silicon-on-insulator MOSFETs is developed to investigate the short-channel effects (SCEs). Our model includes the effects of the source/drain and body doping concentrations, the lengths of the gate metals and their work functions, applied drain and substrate biases, the thickness of the gate and buried oxide and also the silicon thin film. We demonstrate that the surface potential in the channel region exhibits a step function that ensures the screening of the drain potential variation by the gate near the drain resulting in suppressed SCEs like the hot-carrier effect and drain-induced barrier-lowering (DIBL). The model is extended to find an expression for the threshold voltage in the submicrometer regime, which predicts a desirable "rollup" in the threshold voltage with decreasing channel lengths. The accuracy of the results obtained using our analytical model is verified using 2-D numerical simulations.

https://web.iitd.ac.in/~mamidala/HTMLobj-160/april04.pdf

Two-dimensional analytical modeling of fully depleted DMG SOI MOSFET and evidence for diminished SCEs

In this paper, we present the unique features exhibited by a modified asymmetrical double-gate (DG) silicon-on-insulator (SOI) MOSFET. The proposed structure is similar to that of the asymmetrical DG SOI MOSFET with the exception that the front gate consists of two materials. The resulting modified structure, i.e., a dual-material double-gate (DMDG) SOI MOSFET, exhibits significantly reduced short-channel effects (SCEs) when compared with the DG SOI MOSFET. SCEs in this structure have been studied by developing an analytical model. The model includes the calculation of the surface potential, electric field, threshold voltage, and drain-induced barrier lowering. A model for the drain current, transconductance, drain conductance, and voltage gain is also discussed. It is seen that SCEs in this structure are suppressed because of the perceivable step in the surface-potential profile, which screens the drain potential. We further demonstrate that the proposed DMDG structure provides a simultaneous increase in the transconductance and a decrease in the drain conductance when compared with the DG structure. The results predicted by the model are compared with those obtained by two-dimensional simulation to verify the accuracy of the proposed analytical model.

https://web.iitd.ac.in/~mamidala/HTMLobj-248/March05NANO.pdf

A new dual-material double-gate (DMDG) nanoscale SOI MOSFET-two-dimensional analytical modeling and simulation

In this paper, we present the unique features exhibited by modified asymmetrical Double Gate (DG) silicon on insulator (SOI) MOSFET. The proposed structure is similar to that of the asymmetrical DG SOI MOSFET with the exception that the front gate consists of two materials. The resulting modified structure, Dual Material Double Gate (DMDG) SOI MOSFET, exhibits significantly reduced short channel effects when compared with the DG SOI MOSFET. Short channel effects in this structure have been studied by developing an analytical model. The model includes the calculation of the surface potential, electric field, threshold voltage and drain induced barrier lowering. A model for the drain current, transconductance, drain conductance and voltage gain is also discussed. It is seen that short channel effects in this structure are suppressed because of the perceivable step in the surface potential profile, which screens the drain potential. We further demonstrate that the proposed DMDG structure provides a simultaneous increase in the transconductance and a decrease in the drain conductance when compared with the DG structure. The results predicted by the model are compared with those obtained by two-dimensional simulation to verify the accuracy of the proposed analytical model.

A New Dual-Material Double-Gate (DMDG) Nanoscale SOI MOSFET - Two-dimensional Analytical Modeling and Simulation

A generic new type of field effect transistor (FET), the dual material gate (DMG) FET, is proposed and demonstrated. The gate of the DMGFET consists of two laterally contacting materials with different work functions. This novel gate structure takes advantage of material work function difference in such a way that the threshold voltage near the source is more positive than that near the drain (for n-channel FET, the opposite for p-channel FET), resulting in a more rapid acceleration of charge carriers in the channel and a screening effect to suppress short-channel effects. Using the heterostructure FET as a vehicle, the principle, computer simulation results, design guidelines, processing, and characterization of the DMGFET are discussed in detail.

Dual-material gate (DMG) field effect transistor

Highly sensitive and integrated optical multi-band CO2 sensors are significant at the shortwave infrared (SWIR) region and still lack research. A compact CO2 sensor composed of a Au-disk/TiO2-cylinder/Au-film metasurface coated by polyhexamethylene biguanide (PHMB) film, functioning at multi-band resonances as well as having high sensitivity to gas concentrations, is presented. It can be employed as a dual-band narrowband absorber, producing two strongly resonant modes at the SWIR region under a reflection-type framework of linearly polarized incidence. Moreover, the metasurface sensor possesses high refractive index sensitivity of 109.25 pm/ppm at around 1040 nm and 42.57 pm/ppm at around 1330 nm in the range of 200–600 ppm, which is suitable for detecting atmospheric CO2. Furthermore, the numerical results show that the sensitivity increases with a thicker PHMB film and optimizes at a thickness above 600 nm. The physical mechanism reveals that the higher order mode exhibits more extended near-field energy than the lower order mode, resulting in more sensitivity towards the surroundings. The design and results of our investigation show high-quality CO2 sensing performance which functions at dual spectrum bands in the SWIR region and is promising for integrated photonic applications.

/pdf/a-dual-band-carbon-dioxide-sensor-based-on-metal-tio2-metal-2lhokku6.pdf

A Dual-Band Carbon Dioxide Sensor Based on Metal–TiO2–Metal Metasurface Covered by Functional Material

In recent years, perovskite solar cells have achieved high efficiency in small areas, but the industrialization of perovskite solar cells is still hampered by the efficiency loss of cells during area scaling. Series modules are currently the most widely used and effective modular process for perovskite solar cells, a process that requires the patterning of the layer stack in individual cells. This interconnection scheme consists of three lines, P1–P3, which are ablated using a pulsed laser beam. In this work, we developed an efficient perovskite module with a high geometric fill factor (GFF) based on a two-step spin-coating method by optimizing the laser ablation step. We constructed the entire device structure by means of a picosecond green pulsed laser, meanwhile, the dead area is greatly reduced by optimizing the parameters and process, and finally achieving an ultra-high GFF of over 99%. In addition, we investigated the effect of poor P2 and P3 ablation on the perovskite solar modules and compared the performance of the module before and after ablation optimization. We finally obtained a maximum photoelectric conversion efficiency of 22.79% with an aperture area of 12.6 cm2. Concurrently, we conducted electrocatalytic hydrogen production experiments on the prepared perovskite solar modules, and the experimental results have also shown excellent performance and good prospects.

/pdf/preparation-of-high-geometric-filling-factor-perovskite-3iqxqf1h.pdf

W. Long

Papers

Dual-material gate (DMG) field effect transistor

A Dual-Band Carbon Dioxide Sensor Based on Metal–TiO2–Metal Metasurface Covered by Functional Material

Preparation of High Geometric Filling Factor Perovskite Module and Feasibility Study on Electrocatalytic Hydrogen Production