Abstracts:In this paper, versatile triple-level cell (TLC) NAND flash memory control with four proposed techniques, Read-Hot/Cold Migration, Read Voltage Control (RVC), Edge Word-Line Protection (EWLP), and Worst Page Detection (WPD), is proposed for data center application solid-state drives (SSDs). To apply the optimal reliability enhancement techniques for stored data, first proposal of Read-Hot/Cold Migration separates read-hot/cold data into each region. Then, second proposal, Read Voltage Control applies the optimal read reference voltages (V REF) for each read-hot/cold region to improve the overall reliability of TLC NAND flash. Third proposal, Edge Word-Line Protection reduces the bit error rate (BER) of the edge word-lines (WLs), which have the worst reliability in read-hot data as reported in this paper. Finally, Worst Page Detection is proposed to predict the worst page BER in a block precisely to prevent judging entire block as bad and optimizes the refresh interval of read-hot block. By combining all of these techniques, the reliability of TLC NAND flash is enhanced for both read-hot and cold data.

Abstracts:We have fabricated and characterized Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As pseudomorphic high-electron-mobility-transistors (PHEMTs) on a 3-inch InP substrate. Stepper-based photo-lithography was used in all the process steps for device fabrication, aiming to miniaturize key device geometries, such as gate-to-source and gate-to-drain spacing. The fabricated device with Lg = 0.5 μm exhibits an excellent maximum transconductance (gm_max) of 1.9 S/mm at VDS = 1.5 V and an ON-resistance (RON) of below 0.4 Ω-mm. A high value of gm in our device leads to a fantastic combination of current-gain cut-off frequency (fT) of 120 GHz and maximum oscillation frequency (fmax) of 366 GHz at VDS = 0.8 V. These remarkable characteristics stem from the compact geometry design of the In0.52Al0.48As/In0.7Ga0.3As PHEMTs with LGS = LGD = 0.4 μm, coupled with an optimized gate recess process that yields tight control of side-recess spacing (Lside). More importantly, the product of fT and Lg in this work yields 60 GHz-μm which is the highest in any field-effect-transistor (FET) technology on any material system.

Abstracts:The amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) current – voltage (I-V) characteristics can be significantly distorted by either series resistance, RS, associated with the source/drain (S/D) contact regions or/and density of states. To isolate Rs contribution we used the five terminals coplanar homojunction TFT structure. Experimental results have shown this device structure has a low S/D contact resistance that do not contribute to observed I-V nonlinearity. We have shown using combination of the experimental data and two- dimensional simulations that the observed nonlinearity can be associated with the conduction band-tail states.

Abstracts:We propose a specialized gate-drain separation structure for use in investigation of the dynamic behavior of the thermal transport characteristics in AlGaN/AlN/GaN heterojunction transistors. Using this structure, the influence of the two-dimensional electron gas (2DEG) on the horizontal heat transfer in these transistors was identified experimentally. A temperature delay (i.e., the difference in temperature at the same time) of 1.3 °C, which accounts for 8.6% of the total temperature rise, was calculated to be caused by a 0.3 μm $\times$ 150 μm 2DEG depleted region. In addition, the temperature transients show that the 2DEG can accelerate the temperature to the steady state. Infrared measurements were also carried out to benchmark the results. In particular, the sample structure allows the measurement of a complete thermal process that includes both heating and cooling without interruption. Based on a comparison of the two processes, we demonstrated and corrected an error in the temperature rise that occurred when the Schottky junction voltage was used as the temperature-sensitive parameter.

Abstracts:Estimation of threshold voltage $V_T$ variability for NWFETs has been computationally expensive due to lack of analytical models. Variability estimation of NWFET is essential to design the next generation logic circuits. Compared to any other process induced variabilities, Metal Gate Granularity (MGG) is of paramount importance due to its large impact on $V_T$ variability. Here, an analytical model is proposed to estimate $V_T$ variability caused by MGG. We extend our earlier FinFET based MGG model to a cylindrical NWFET by satisfying three additional requirements. First, the gate dielectric layer is replaced by Silicon of electro-statically equivalent thickness using long cylinder approximation; Second, metal grains in NWFETs satisfy periodic boundary condition in azimuthal direction; Third, electrostatics is analytically solved in cylindrical polar coordinates with gate boundary condition defined by MGG. We show that quantum effects only shift the mean of the $V_T$ distribution without significant impact on the variability estimated by our electrostatics-based model. The $V_T$ distribution estimated by our model matches TCAD simulations. The model quantitatively captures grain size dependence with $\sigma (V_T)$ with excellent accuracy ($6\%$error) compared to stochastic 3D TCAD simulations, which is a significant improvement over the state-of- the-art model with fails to produce even a qualitative agreement. The proposed model is $63\times$ faster compared to commercial TCAD simulations.

Abstracts:Detailed analysis of device behaviour on the zero-temperature coefficient (ZTC) points for microwave GaAs based high-electron mobility transistor is presented by means of on-wafer measurements over the temperatures between −40 and 150 °C. This zero temperature coefficient points found not only in the transfer and transconductance curve but also in intrinsic transconductance gmo, output conductance gds, small signal gain S21, and minimum noise figure NFmin also exhibits ZTC. It is found that the zero temperature coefficients points are impacted by both threshold voltage and drain bias. The transfer current base, ZTCIds moved from 0.1 V to −0.2 V of Vgs trace and transconductance based, ZTCgm moved from −0.3 V to −0.6 V of Vgs trace with the drain bias, Vds varies from 1 V to 5 V. The behaviour of some intrinsic equivalent circuit parameters along with cut-off frequency, f t at both ZTC bias points opens some crucial insight and opportunities in microwave device design for low and high temperature applications.

Abstracts:Although metallic nanostructures in solar cells provide versatility in designing useful plasmonic architectures, understanding is still limited on how to exploit their multi-scale contribution as tunable performance. In this article, we suggest a characteristic model that develops into a simple and robust tool for guiding optimization of plasmonic solar devices. The model is conceptually based on the breakdown of the active region into intrinsic and plasmonic sub-circuits, by which the terminal currents are directly correlated with particle geometries and local improvement. Measurements from organic cells support the validity of our theory, and a series of simulation provides further insights into the critical trade-off between voltage and current generation, finally offering a strategy for efficiency enhancement.

Abstracts:Current-voltage (I-V) properties of indium-tin-oxide/Ag nanoparticles embedded in polyurethane film/Al devices exhibited a current bistability with ON/OFF ratio within the range of 10⁵–10³ with the variation of voltage from −0.85 to 3.95 V, which was nearly 10² larger than that for the device without Ag nanoparticles. The memory margin was obviously enlarged due to the existence of the Ag nanoparticles embedded in the polyurethane layer. I-V properties and write-read-erase-read voltage cycles test indicated the flash resistive switching properties. The data retention time reach up to 1.8 × 10⁴ s, which manifested the stability of the memory devices. I-V property at ON state was attributed to the drift mechanism, and the property at OFF state was related to the space-charge-limited-current behaviors.

Abstracts:In order to improve the microstructure and sensing property for electrode material BiVO4 of potentiometric ammonia sensor, different MgO-doped (0, 1, 3, 5 and 8 at.%) BiVO4 powders were synthesized by solid-state reaction method. There is no significant difference in XRD spectrum for the different powders, but the particle size of the sensing electrode has an obvious refinement with the doping of MgO. The NH3 sensitivity of the sensor had a enhancement from 41.7 mV/decade to the highest value of 61.8 mV/decade when Mg-content reaches 5 at.%. The interfacial resistance Ri between the electrode and YSZ decreases with the increment of NH3 concentration and the Mg-doping based on impedance spectroscopy. The reduction of interface resistance is due to the enhancement of electrode reactions. The dopant MgO improves the conductivity of BiVO4 and the TPB area, and leads to a greater charge exchange rate for the electrode electrochemical reactions. The increased specific surface area due to the grain size refinement gets more NH3 involved in the reactions. This eventually leads to the increased sensitivity and decreased interface resistance. The optimal operating temperature is 600 °C based on the synthetical effects of various factors such as conductivity, the catalytic and gas adsorption performances of the sensing material.

Abstracts:We demonstrated an Au-free ohmic contact for un-doped AlGaN/GaN HEMTs with Ti/Al/Ti/TiW metal structure. The Au-free ohmic contact was fabricated by pre-ohmic recess etching and low annealing temperature. The contact characteristics of the Ti/Al/Ti/TiW Au-free ohmic contacts including current-voltage, contact resistivity, and microstructure are systematically investigated. The contact resistivity of Ti/Al/Ti/TiW ohmic contact with 22-nm recessed depth and 600 °C annealing temperature is 5.44 × 10⁻⁵ Ω⋅cm², which is comparable with conventional Ti/Al/Ni/Au ohmic contact. In addition, the Ti/Al/Ti/TiW ohmic contact shows smooth surface morphology with an excellent surface roughness of 3.69 nm. Besides, AlGaN/GaN MISHEMTs based on Ti/Al/Ti/TiW Au-free low temperature ohmic contacts were fabricated and exhibited good DC characteristics. The reported Au-free AlGaN/GaN HEMT fabrication process can be used in standard Si fabs without the risk of contamination.