Amitava Das Gupta

Micropumps form the heart of several microfluidic systems like micro total analysis system (µTAS) and drug delivery devices, which have resulted from the advancement of silicon micromachining technology. Among the different available types of micropumps, valveless micropumps are better suited for biological applications as they do not have flow-rectifying valves and are less prone to clogging and wear. However, their main drawback is low thermodynamic efficiency. This can be improved if we have a better understanding of the effects of geometry on the performance. This forms one of the objectives of this work. This chapter describes the activity on the design and development of valveless micropumps. A numerical parametric study of the performance of valveless micropumps has been carried out and is presented to bring out the effects of different geometrical parameters. Based on these design approaches, silicon-based micropumps are fabricated and characterized. The performance of one of these micropumps is compared with designed value in this work.

In this paper, a semi-analytical model is derived to calculate the anchor loss of TPoS resonators operating in higher-order length extensional modes. This model provides valuable insights on the effect of order, device dimensions, position and number of anchors on the quality factor (Q) of these resonators. Results from this model are in close agreement with the FEM simulations. The optimum position, dimension, and the number of anchors to deliver the highest Q are also discussed. Predictions of the model are validated through characterization of TPoS resonators fabricated to operate at a resonant frequency of around 1 GHz with different number of anchor pairs and position. A 23rd order resonator with a W/L ratio of 1.5 with three pairs of anchors placed at positions suggested by the model gave a loaded Q of 4431, which is 65% more than the conventional case where anchors are uniformly placed towards the edge, and also an improvement in the insertion loss by 5.5 dB compared to the latter. For resonators where the anchor loss is predominant, our results show that the performance can be improved by placing the anchors at the optimum position, closer to the middle of the resonator than the conventional scheme where anchors are uniformly placed towards the edge.

A unified model for gate capacitance-voltage characteristics of Si/SiGe heterostructure pMOSFETs is presented. This model is applicable to buried-channel, surface-channel, and dual-channel Si/SiGe heterostructure pMOSFETs. The results from the model are compared with the experimental results and are found to be in excellent agreement. A simple and accurate method for the extraction of parameters such as the valence band offset, Si cap layer thickness, threshold voltages, and substrate doping is also presented in this paper. © 2007 IEEE.

Dependence of gate leakage current on Al mole fraction of AlGaN/GaN high-electron mobility transistors (HEMTs) is studied using temperature-dependent current-voltage and capacitance-voltage characteristics. The reverse leakage current is mostly dominated by Poole-Frenkel (PF) emission in the structures used in this brief. However, it is observed that at higher mole fractions, due to higher electric field across the barrier, Fowler-Nordheim (FN) tunneling also contributes to the gate leakage current even at room temperature and above. An expression for critical temperature below which FN tunneling component becomes comparable with or more than PF emission component is presented. It is concluded that the dominant gate leakage mechanisms in III - N HEMTs are dependent on mole fraction of the barrier material and the temperature. However, the relative strengths of PF emission and FN tunneling are also influenced by various process-dependent parameters.

Transdermal drug delivery (TDD), which enables targeted delivery with microdosing possibilities, has seen much progress in the past few years. This allows medical professionals to create bespoke treatment regimens and improve drug adherence through real-time monitoring. TDD also increases the effectiveness of the drugs in much smaller quantities. The use of polymers in the drug delivery field is on the rise owing to their low cost, scalability and ease of manufacture along with drug and bio-compatibility. In this work, we present the design, development and characterization of a polymer-based TDD platform fabricated using additive manufacturing technologies. The system consists of a polymer based micropump integrated with a drug reservoir fabricated by 3D printing and a polymer hollow microneedle array fabricated using photolithography. To the best of our knowledge, we present the fabrication and characterization of a 3D-printed piezoelectrically actuated non-planar valveless micropump and reservoir integrated with a polymer hollow microneedle array for the first time. The integrated system is capable of delivering water at a maximum flow rate of 1.03 mL/min and shows a maximum backpressure of 1.37 kPa while consuming only 400 mW. The system has the least number of moving parts. It can be easily fabricated using additive manufacturing technologies, and it is found to be suitable for drug delivery applications.

In this article, the effect of charge partitioning in a silicon-on-insulator lateral double-diffused metal-oxide-semiconductor (LDMOS) transistor on its nonlinearity model is investigated. It is found that the prediction of the third-order intermodulation distortion (IM3) depends on the model equivalent circuit (EC) and appropriate charge assignments at various nodes therein. The investigation is carried out using a highly accurate static model of LDMOS along with a couple of different charge-partitioning schemes in order to single out their effects on the nonlinearity model behavior. We observe that charge partitioning in a more flexible EC framework yields an improved IM3 prediction when compared with the TCAD simulated results.

In this paper we present the design and process optimization for fabricating piezoresitive pressure sensor and MOSFET Differential Amplifier simultaneously on the same chip. Silicon On Insulator approach has been used for realizing the membrane as well as the electronics on the same chip. The amplifier circuit has been configured in the common source connection and it has been designed with PSPICE simulation to achieve a voltage gain of about 5. In the initial set of experiments the Pressure sensor and the amplifier were fabricated on separate chips to optimize the process steps and tested in the hybrid mode. In the next set of experiments, SOI wafer having the SOI layer thickness of about 11 microns was used for realizing the membrane by anisotropic etching from the backside. The piezo-resistive pressure sensor was realized on this membrane by connecting the polysilicon resistors in the form of a Wheatstone bridge. The MOSFET source follower amplifier was also fabricated on the same SOI wafer by tailoring the process steps to suit the requirement of simultaneous fabrication of piezoresistors and the amplifier for achieving MOSFET Integrated Pressure Sensor. Reproducible results have been achieved on the SOI wafers, with the process steps developed in the laboratory. Sensitivity of 270 mV /Bar/10V, with the on chip amplifier gain of 4.5, has been achieved with this process. © 2006 IOP Publishing Ltd.

In this work, the effects of physical dimensions such as length, width and thickness as well as the mode of vibration and the number of anchors on the performance of longitudinal thin film piezoelectric on silicon (TPoS) MEMS resonators have been studied. TPoS resonators, designed for a resonant frequency of around 1 GHz, were fabricated with a 4 mask CMOS compatible process. A 225μ m wide resonator excited in its 23rd order had an unloaded quality factor of 9453 (in vacuum), which is the highest value reported so far for similar resonators, motional resistance of 107Ω and linear thermal coefficient of frequency of-28.4 ppm. We have also studied and modeled the different loss mechanisms in these devices. The model matches well with measured results for resonators of different geometries, modes of vibrations and number of anchors. [2020-0397].

An analytical Thermionic-Field- Diffusion Model for the current transport in a Heterostructure Emitter Bipolar Transistor (HEBT) is presented for the first time. The results obtained from the model show good agreement with reported experimental data. The performances of HEBTs are compared with corresponding HBTs using the developed model. It is shown that the HEBTs show higher common emitter current gains compared to that of HBTs at the same current density. The effect of the lower bandgap emitter thickness on the current gain of HEBTs is studied.

MOS capacitors with ultrathin (≅1.2 nm) oxide grown by different techniques have been fabricated on Strained Si/Relaxed SiGe/n-Si substrates with linearly graded SiGe. These techniques involve thermal oxidation, chemical oxidation and both followed by anodic oxidation. Significant improvement in interface states has been obtained when oxidation was followed by anodic oxidation. The leakage currents and reliability characteristics have also shown great improvement. Band gap offsets extracted using a simple and novel technique are found to match well with expected values. © 2007 IEEE.