Shubhankar Majumdar

Simplified gas sensor model based on AlGaN/GaN heterostructure Schottky diode

Physics based modeling of AlGaN/GaN heterostructure Schottky diode gas sensor has been investigated for high sensitivity and linearity of the device. Here the surface and heterointerface properties are greatly exploited. The dependence of two dimensional electron gas (2DEG) upon the surface charges is mainly utilized. The simulation of Schottky diode has been done in Technology Computer Aided Design (TCAD) tool and I-V curves are generated, from the I-V curves 76% response has been recorded in presence of 500 ppm gas at a biasing voltage of 0.95 Volt.

Artificial neural network modelling of ADS designed Double Pole Double Throw switch

An alternative approach for designing a DPDT switch and characterizing it with the help of ANN modelling is presented in this work. ANN is one of the options which can be implemented to model the output parameters obtained from the designed switch. As, it does not require any detailed physical models, only a few training points are required to accurately model the standards. In this work, the DPDT switch circuit has been designed using ADS through UMS 0.15 μm pHEMT process design kit. Neural network training has been done using Levenberg-Marqaurdt back propagation algorithm employed in the ANN toolbox of MATLAB software. The outcome of simulated results in an ADS designed switch indicates an isolation of -31 to -17 dB, an insertion loss of -1.15 to -0.8 dB, a noise figure of 0.4 to 0.38 and port return loss of -8.44 to -14.36 dB for a frequency level of 1 to 5 GHz. All the results obtained from ADS simulation have been validated using ANN modelling, and it shows a close agreement with a mean squared error of about 10-8.

Evaluating substrate's effect on RF switch performance via Verilog-A GaN HEMT model

Fabrication and RF characterization of GaN HEMT on silicon and sapphire substrate are done, and henceforth, forming a Verilog-A model by experimental results obtained from RF characterization of GaN HEMT. This model is implemented for designing of RF switch in Cadences spectre, to evaluate the substrate effects on RF switch performance. The variation in isolation, insertion loss, and return loss for a frequency range of 2.5GHz is found as 15dB/10dB, 3dB/2.2dB, and 0.7dB/0.4dB for silicon/sapphire substrate, respectively. Fabrication and RF characterization of the GaN HEMT on silicon (Si) and sapphire (Al2O3).Proposes a novel way to include the experimental data in the circuit simulator for circuit design.Implementation of VerilogA model for determining the impact of different substrates on the RF switch characteristics.

Hardwired BIST architecture of SRAM

This work proposed an on-chip architectural design, validation and feasibility of a BIST for 8×8 SRAM using 0.18 μm UMC technology in Cadence Virtuoso and Spectre Tool for storage and retrieval faults detection. As, the technology shrinks and share of memories in complex systems increases, memories become susceptible to faults. Storage and retrieval faults are genuinely faced by SRAM. This type of fault occurs due to improper storage or retrieval of data i.e. breakage in the word line or in bit line. Thus, it become a major issue for test engineers, as area overhead is a constraint. From the results obtained, it has been observed that the proposed architecture, for detecting the storage and retrieval faults is working properly but the area and power due to BIST is increased with comparison to the circuit under test alone. The feasibility of proposed BIST architecture is checked by calculating the area and power overhead of BIST for large size memories.

Analysis of strain induced carrier confinement with varying passivation thickness of the Al0.3Ga0.7N/GaN heterostructure with graded AlxGa1-xN buffer on Si (111) substrate

In this study, the authors demonstrate the strain induced piezoelectric charge effect on carrier confinement at the Al0.3Ga0.7N/GaN heterointerface with varying passivation (Si3N4) thicknesses. The graded Al0.2Ga0.8N/Al0.1Ga0.9N buffer on the Si (111) substrate grown by plasma assisted molecular beam epitaxy reduces the dislocation density of the GaN layer, which significantly improves the carrier concentration at the Al0.3Ga0.7N/GaN interface. The carrier confinement as well as the two-dimensional electron gas (2DEG) density with varying passivation thicknesses has been investigated through high resolution x-ray diffraction (HRXRD) followed by strain analysis and capacitance–voltage (C-V) measurements. As per the HRXRD strain analysis, the 2DEG density was predicted to increase about 5%, 7.9%, and 10% after Si3N4 passivation of 20, 30, and 40 nm, respectively. This enhancement in carrier density (2DEGs) was then validated by C-V characteristics for the same Si3N4 variation. After passivation, the induced...

Temperature dependent etching of Gallium Nitride layers grown by PA -MBE

Future of microwave, power and photonics industry is focused on GaN due to its extraordinary material properties such as wide and direct band gap, large thermal and chemical stability, high breakdown voltage, high saturation velocity. Formation of devices for these applications requires a material selective etching which is performed via wet-etching process. In this paper, temperature dependent etching properties of GaN have been revealed. Molten KOH has been employed as an etchant, to etch 2 μm MBE grown GaN layer on Silicon (111). To verify temperature dependence of GaN etching, etching has been performed at a fixed concentration and etching time. Optimum temperature to etch GaN completely has been determined from Arrhenius plot of etch rate vs temperature. Etch depth has been determined from AFM, whereas, morphology has been confirmed using SEM.