Department of Electrical Engineering

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IIT Jodhpur

The presence of dielectric charging in a switch causes stiction and drift in pull-in voltage. A design to alleviate charging issues for RF MEMS switches is proposed. An RF MEMS capacitive switch has been fabricated and characterized. Measured pull-in of the switch is <20 V and pull-up voltage is 17 V with a switching time of 78 μs. Insertion loss and isolation of the switch are measured by varying RF power from 0 to 15 dBm at room temperature. Insertion loss and isolation of the switch are better than 0.1 and 17 dB, respectively. Resonant frequency of the device is 8.4 kHz. The switch has completed 600 million cycles. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).

World University root node

Journal of Micro/ Nanolithography, MEMS, and MOEMS

Reduced dielectric charging RF MEMS capacitive switch

In this paper, fabrication of a rectangular paddle micro-cantilever-based wind speed sensor along with its analytical model has been presented. The analytical model uses the closed-form solution to the bending stress caused by static deflection. Simulations of the device were done using finite-element analysis. The simulation, analytical, and experimental results have been compared for a better insight into the sensor behavior. Piezo-resistive deflection detection mechanism has been utilized to measure the wind speed. The experimental results show that the fabricated sensor can detect wind speed up to 29 ms-1 and has a sensitivity of 0.071 mV/ms-1 - V. © 2018 IEEE.

IEEE Sensors Journal

Analytical Modeling, Simulation, and Fabrication of a MEMS Rectangular Paddle Piezo-Resistive Micro-Cantilever-Based Wind Speed Sensor

A detailed experimental investigation on nanostructured tungsten trioxide (WO3) based bottom gate field effect transistor (FET) is presented. These were fabricated using scalable process and thoroughly characterized for morphology and device performance. It was also observed that thickness of WO3 and ambient during annealing played a key role in tuning the morphology. The transistors bearing nanostructured morphology of WO3 were tested for device performance such as input-output and transfer characteristics at low, room, and high temperatures. Of all the devices tested, best on-off ratio obtained was 105 and sub-threshold slope obtained was 150 mV/decade inferring an efficient performance of the FET. A tradeoff between the on-off ratio (ION/IOFF) and sub-threshold slope was noticed at higher temperatures. This was attributed to the ambipolar nature of the WO3 films. At a given temperature and bias, either the holes or electrons were present for transport and conduction. Such ambipolar films find great potential in transistors that can be used in switching applications. © 2018 IEEE.

IEEE Transactions on Nanotechnology

Temperature Dependent Electrical Characteristics of Nanostructured WO3 Based Ambipolar Bottom Gate FET

Negative capacitance field effect transistor (NCFET) is designed in 5-nm FinFET node, which simultaneously meets the low-power and high-performance targets of ION and IOFF at Vdd = 0.5 V and Vdd = 0.23 V, respectively, while the international roadmap for devices and systems (ITRS 2.0) projected Vdd is 0.65 V for both. The impact of power supply and parasitic capacitance on the performance of NCFET is studied. It is demonstrated that NCFET can be designed for fluid subthreshold swing (SS) behavior such that SS is degraded around Vgs = 0, Vds = Vdd, and is improved in the subthreshold region. This helps in combating OFF-current variation due to the threshold voltage fluctuations. A compact model to determine such design conditions is presented. Parasitic capacitance and the ferroelectric material parameters should be cooptimized for the target Vdd. © 1963-2012 IEEE.

IEEE Transactions on Electron Devices

Designing 0.5 v 5-nm HP and 0.23 v 5-nm LP NC-FinFETs with Improved IOFF Sensitivity in Presence of Parasitic Capacitance

Anomalous transconductance with nonmono-tonic back-gate bias dependence observed in the fully depleted silicon-on-insulator (FDSOI) MOSFET with thick front-gate oxide is discussed. It is found that the anomalous transconductance is attributed to the domination of the back-channel charge in the total channel charge. This behavior is modeled with a novel two-mobility model, which separates the mobility of the front and back channels. These two mobilities are physically related by a charge-based weighting function. The proposed model is incorporated into BSIM-IMG and is in good agreement with the experimental and simulated data of FDSOI MOSFETs for various front-gate oxides, body thicknesses, and gate lengths. © 1963-2012 IEEE.

New Mobility Model for Accurate Modeling of Transconductance in FDSOI MOSFETs

We present a charge-based compact model for induced gate thermal noise for a fully depleted silicon-on-insulator transistor. The model uses front- and back-gate charges as well as the respective mobilities for the development of analytical expression. The model is implemented in Verilog-A and validated with experimentally calibrated TCAD simulations. The model predicts the high-frequency behavior with good accuracy while capturing the back-bias dependence. © 2001-2012 IEEE.

IEEE Microwave and Wireless Components Letters

Modeling of Induced Gate Thermal Noise Including Back-Bias Effect in FDSOI MOSFET

In negative capacitance field-effect transistors (NCFETs), drain current may decrease with increasing Vds in the saturation region, leading to negative differential resistance (NDR). While NDR is useful for oscillator design, it is undesirable for most analog circuits. On the other hand, the tendency toward NDR may be used to reduce the normally positive output conductance (gds) of a short-channel transistor to a nearly zero positive value to achieve higher voltage gain. In this paper, we analyze the NDR effect for NCFET in the static limit and demonstrate that it can be engineered to reduce gds degradation in short-channel devices. Small and positive gds is achieved without compromising the subthreshold gain, which is crucial for analog applications. The 7-nm ITRS 2.0 FinFET with 0.7 V Vdd is used as the baseline device in this paper. © 1963-2012 IEEE.

Engineering negative differential resistance in NCFETs for analog applications

We demonstrate an efficient ultra-broadband supercontinuum generation in telecom-grade optical fiber by pumping Q-switched subnanosecond laser pulses (0.77 ns) at 1064 nm in the normal dispersion region of the fiber. The fiber supports several spatial modes at this pump wavelength. Multiple sidebands with six Raman stokes spanning over more than 1100 nm (starting well below 600 nm and extending beyond 1700 nm) are generated using very low input pump power (average 57 mW). Theoretical analysis shows that cascaded Raman and cascaded intermodal four-wave mixing processes can account for the generation of multiple sidebands. We also demonstrate that the modal composition of the input pump profile can provide an extra degree of freedom in tailoring the multiple Raman peaks in the output spectrum. © 1983-2012 IEEE.

Journal of Lightwave Technology

Cascaded Raman and Intermodal Four-Wave Mixing in Conventional Non-Zero Dispersion-Shifted Fiber for Versatile Ultra-Broadband Continuum Generation

We show an all-fiber multimode interference method for achieving pre-determined free-space propagation of multimode optical beams exiting from the fiber end-facet. This method provides independent control over the relative amplitudes and the relative phase difference between the LP0,1 and LP0,2 modes of the output few-mode fiber, ensuring predictable free-space propagation behavior. We also show that the LP0,1 beam suffers greater unpredictability in the free-space propagation as compared to the LP0,2 beam if the phase difference between the two modes is not controlled. The negative effect of mode-mixing can be avoided if both the modes are in-phase at the fiber end-facet. We also demonstrate significant features in the free-space propagation behavior for different optical beams, justifying the theory. © 2018 Optical Society of America.

Journal of the Optical Society of America B: Optical Physics

Design of an all-fiber multimode-interference-based multimode optical beam generator: Theory and experiment

A novel polarization diverse substrate integrated waveguide (SIW)-based leaky-wave antenna (LWA) is proposed for larger radiation coverage by frequency beam scanning in X-band. For feeding purpose, the SIW-based power divider, the directional coupler, and the 180° power splitter are used in the design. For radiation, +45°/-45° tilted slots are etched on top and bottom faces of the structure such that the radiated quad beam scans all the four quadrants. By varying the means of excitation at two input ports, multiple polarization states are realized. The antenna shows ±45° dual polarization (+45° and -45° are co-existing), horizontal and vertical polarization, and two types of circular dual-polarization (left handed and right handed simultaneously). The proposed antenna is capable of scanning in each of the four quadrants simultaneously with the scanning range of 62° having the maximum gain of 12.6 dBi and an improved cross-polarization level better than -20 dB. The quad beam covers overall scanning range of 248° with different polarization states. The S-parameters, radiation patterns, gain, and axial ratio are calculated and demonstrated. The proposed LWA shows desirable advantages, such as simultaneous four-quadrant frequency beam scanning having polarization diversity capabilities, which leads to a flexible design for practical utilization. © 1963-2012 IEEE.