Threshold Voltage Model for a Fully Depleted SOI-MOSFET with a Non-Uniform Profile

A novel approximation of the two-dimensional （2D） potential function perpendicular to the channel is proposed,and then an analytical threshold voltage model for a fully depleted SOI-MOSFET with a non-uniform Gaussian distribution doping profile is given based on this approximation. The model agrees well with numerical simulation by MEDICI. The result represents a new way and some reference points in analyzing and controlling the threshold voltage of non-uniform fully depleted （FD） SOI devices in practice.

An Analytical Threshold Voltage Model for Fully Depleted SOI MOSFETs

A new two-dimensional （2D） analytical model for the threshold-voltage of fully depleted SOI MOSFETs is derived. The 2D potential distribution functions in the active layer of the devices are obtained through solving the 2D Poisson＇s equation. The minimum of the potential at the oxide-Si layer interface is used to monitor the threshold voltage of the SOI MOSFETs. This model is verified by its excellent agreement with MEDICI simulation using SOI MOSFETs with different gate lengths,gate oxide thicknesses,silicon film thicknesses,and channel doping concentrations.

A Temperature-Dependent Model for Threshold Voltage and Potential Distribution of Fully Depleted SOI MOSFETs

A temperature-dependent model for threshold voltage and potential distribution of fully depleted silicon-on- insulator metal-oxide-semiconductor field-effect transistors is developed. The two-dimensional potential distribution function in the silicon thin film based on an approximate parabolic function has been applied to solve the two-dimensional Poisson＇s equation with suitable boundary conditions. The minimum of the surface potential is used to deduce the threshold voltage model. The model reveals the variations of potential distribution and threshold voltage with temperature, taking into account short-channel effects. Furthermore, the model is verified by the SILVACO ATLAS simulation. The calculations and the simulation agree well.

Simulation Study of Nanoscale FDSOI MOSFET Characteristics

Silicon on insulator (SOI) technology permits a good solution to the miniaturization as the MOSFET size scales down. This paper is about to compare the electrical performance of nanoscale FD-SOI MOSFET at various gate lengths. The performance is compared and contrasted with the help of threshold voltage, subthreshold slope, on-state current and leakage current. Interestingly, by decreasing the gate length, the leakage current and on-state current are increased but the threshold voltage is decreased and the sub-threshold slope is degraded. Silvaco two-dimensional simulations are used to analyze the performance of the proposed structures.

SOICMOS Integrated Circuit of Laser Range Finding Working at High Temperatures

Modeling analysis of thin fully depleted SOICMOS technology has been done. Using ISETCAD software,the high temperature characteristics of an SOICMOS transistor were simulated in the temperature range of from 300 to 600K, and the whole circuit of a laser range finder was simulated with Verilog software. By wafer pro- cessing,a circuit of a laser range finder with complete function and parameters working at high temperatures has been developed. The simulated results agree with the test results. The test of the circuit function and parameters at normal and high temperature shows the realization of an SOICMOS integrated circuit with low power dissipation and high speed, which can be applied in laser range finding. By manufacturing this device, further study on high temperature characteristics of shorter channel SOICMOS integrated circuits can be conducted.

Fully depleted vdW heterojunction based high performance photovoltaic photodetector

Van der Waals(vdW)heterojunctions,with their unique electronic and optoelectronic properties,have become promising candidates for photodetector applications.Amplifying the contribution of the depletion region in vdW heterojunction,which would enhance both of the collection efficiency and speed of the photogenerated carriers,presents an effective strategy for achieving high performance vdW heterojunction photodetectors.Herein,a fully depleted vdW heterojunction photodetector is built on two-dimensional(2D)semiconductor materials(GaTe and InSe)layered on a pattered bottom electrode in vertical structure,in which the generation and motion of carriers are exclusively achieved in the depletion region.Attributed to the intrinsic built-in electric field,the elimination of series resistance and the depletion region confinement of carriers,the as-fabricated photodetector exhibits prominent photovoltaic properties with a high open-circuit voltage of 0.465 V,as well as photoresponse characteristics with outstanding responsivity,detectivity and photoresponse speed of 63.7 A/W,3.88×10^(13)Jones,and 32.7 ms respectively.The overall performance of this fully depleted GaTe/InSe vdW heterojunctions photodetectors are ranking high among the top level of 2D materials based photodetectors.It indicates the device architecture can provide new opportunities for the fabrication of high-performance photodetectors.

Heteromaterial-gate line tunnel field-effect transistor based on Si/Ge heterojunction

A Si/Ge heterojunction line tunnel field-effect transistor （LTFET） with a symmetric heteromaterial gate is proposed. Compared to single-material-gate LTFETs, the heteromaterial gate LTFET shows an off-state leakage current that is three orders of magnitude lower, and steeper subthreshold characteristics, without degradation in the on-state current. We reveal that these improvements are due to the induced local potential barrier, which arises from the energy-band profile modulation effect. Based on this novel structure, the impacts of the physical parameters of the gap region between the pocket and the drain, including the work-function mismatch between the pocket gate and the gap gate, the type of dopant, and the doping concentration, on the device performance are investigated. Simulation and theoretical calculation results indicate that the gap gate material and n-type doping level in the gap region should be optimized simultaneously to make this region fully depleted for further suppression of the off-state leakage current.

Analytical modeling of drain current and RF performance for double-gate fully depleted nanoscale SOI MOSFETs

A new 2D analytical drain current model is presented for symmetric double-gate fully depleted nanoscale SOI MOSFETs.Investigation of device parameters like transconductance for double-gate fully depleted nanoscale SOI MOSFETs is also carried out.Finally this work is concluded by modeling the cut-off frequency, which is one of the main figures of merit for analog/RF performance for double-gate fully depleted nanoscale SOI MOSFETs.The results of the modeling are compared with those obtained by a 2D ATLAS device simulator to verify the accuracy of the proposed model.

X-ray irradiation-induced degradation in Hf_(0.5)Zr_(0.5)O_(2) fully depleted silicon-on-insulator n-type metal oxide semiconductor field-effect transistors

The n-type ultrathin fully depleted silicon-on-insulator(FDSOI) metal-oxide-semiconductor field-effect transistors(MOSFETs),with a Hf_(0.5)Zr_(0.5)O_(2) high dielectric permittivity(high-k) dielectric as gate insulator,were fabricated.The total ionizing dose effects were investigated,and an X-ray radiation dose up to 1500 krad(Si) was applied for both long-and short-channel devices.The short-channel devices(0.025-0.100 μm) exhibited less irradiation sensitivity compared with the long-channel devices(0.35-16 μm),leading to a 71% reduction in the irradiation-induced drain current growth and a 26% decrease in the shift of the threshold voltage.It was experimentally demonstrated that the OFF mode is the worst case among the three working conditions(OFF,ON and A110) for short-channel devices.Also,the determined effective electron mobility was enhanced by 38% after X-ray irradiation,attributed to the different compensations for charges triggered by radiation between the highk dielectric and buried oxide.By extracting the carrier mobility,gate length modulation,and source/drain(S/D)parasitic resistance,the degradation mechanism on X-ray irradiation was revealed.Finally,the split capacitance-voltage measurements were used to validate the analysis.

Digital 1 V 82 μW Pseudo-Two-Stage Class-AB OTA

A low power digital operational transconductance amplifier （OTA） was developed for low voltage switched capacitor applications. The OTA has a high slew rate （SR） and a large open loop gain with a dif- ferential pseudo-two-stage Class-AB structure. A fully compensated depletion mode capacitor is used in the switched capacitor common mode feedback block instead of a metal-insulator-metal （MIM） capacitor to reduce the fabrication cost. Simulations show that with a 1.0-V supply voltage and a 34-pF load at each output terminal, this digital differential pseudo-two-stage Class-AB OTA realized in 0.13-μm technology achieves a 63.5-dB DC gain and a 0.83-V output swing. The slew rate is ±16.29V/μs and the total power dissipation is only 82 μW.

On substrate dopant engineering for ET-SOI MOSFETs with UT-BOX

The importance ofsubstrate doping engineering for extremely thin SOI MOSFETs with ultra-thin buried oxide （ES-UB-MOSFETs） is demonstrated by simulation. A new substrate/backgate doping engineering, lateral non-uniform dopant distributions （LNDD） is investigated in ES-UB-MOSFETs. The effects of LNDD on device performance, Vt-roll-off, channel mobility and random dopant fluctuation （RDF） are studied and optimized. Fixing the long channel threshold voltage （Vt） at 0.3 V, ES-UB-MOSFETs with lateral uniform doping in the substrate and forward back bias can scale only to 35 nm, meanwhile LNDD enables ES-UB-MOSFETs to scale to a 20 nm gate length, which is 43% smaller. The LNDD degradation is 10% of the carrier mobility both for nMOS and pMOS, but it is canceled out by a good short channel effect controlled by the LNDD. Fixing Vt at 0.3 V, in long channel devices, due to more channel doping concentration for the LNDD technique, the RDF in LNDD controlled ES-UB-MOSFETs is worse than in back-bias controlled ES-UB-MOSFETs, but in the short channel, the RDF for LNDD controlled ES-UB-MOSFET is better due to its self-adaption of substrate doping engineering by using a fixed thickness inner-spacer. A novel process flow to form LNDD is proposed and simulated.