Enakshi Bhattacharya

Ultrathin silicon nanoporous membranes with multiple pores were fabricated using batch processes involving chemical vapor deposition and rapid thermal annealing. Transmission electron microscope images showed the existence of nanopores with an average pore size of 13 nm. Measurement of ionic conduction of electrolytes with varying conductivity across the membranes confirmed the existence of pores and the repeatability of the process. The functional diameter of the pores was determined by analyzing the permeability of several industrially and medically important globular biomolecules of varying sizes such as α-amylase, bovine serum albumin, catalase and xanthine oxidase. Biomolecules with hydrodynamic diameters up to 8 nm passed through the nanopores, whereas the passage of the larger molecules was hindered. The surface charges on the molecules determine the functional diameter of the pores, and hence the permeability, as substantiated by varying the pH of the buffer solution. The filtered proteins were found to be uncleaved from sodium dodecyl sulfate polyacrylamide gel electrophoresis, and the enzyme assay of the filtered amylase showed that the activity remained unchanged. © 2002-2012 IEEE.

Over the last decade, silicon nitride (SiN) based integrated photonics has become popular due to its CMOS com-patibility, low loss, wide spectral operation band and tolerance to high optical power. It has great potential in different application areas like quantum information processing, microwave photonics, spectroscopy, etc. However, the growth of an optical grade oxide layer (for bottom cladding) and subsequent deposition of SiN device layer on the surface of a handle silicon wafer are the most important aspects for the realization of large- scale photonic integrated circuits with an acceptable waveguide losses and fabrication yields. In this paper, we report the in- house technology development of SiN waveguide devices starting from a 4- inch silicon wafer. Both the thermally grown buried oxide (BOX) and the LPCVD deposited SiN device layer show excellent uniformities in terms of their thickness $(1900\pm 20nm, 400\pm 4nm$, respectively) as well as refractive indices $(n_{SiO_{2}}= 1.45\pm 0.001, n_{SiN}=2.024\pm 0.003$ at $\lambda\sim 1.55\mu m)$ across the full wafer. We have discussed the design and characterization of the grating coupler, single mode waveguides operating at $\lambda\sim 1.55\mu m$ and their fabrication flow as well. The fabricated single mode waveguides (TE polarized) with input/output grating couplers exhibit a 3-dB bandwidth of $\sim 50nm$ with a peak transmission efficiency at $\lambda\sim 1570nm$. The SiN waveguides fabricated out of in-house processed SiN wafer exhibit reasonable third order non-linearity; confirmed by stimulated four wave mixing experiment.

A wide variety of MEMS micro-mirrors are being developed for various optical applications. One such application is Fourier Transform Spectrometry (FTS). The design, process optimization and fabrication of a micro-mirror for this application is presented. Large, non-tilting displacements of mirrors are required to achieve high FTS resolution. In order to obtain this without using Deep Reactive Ion Etching (DRIE), the micro-mirrors were fabricated on silicon using bulk micromachining techniques. This paper will present the process developed for fabrication of the mirror with the required specifications. In addition, results of the FTS experiments conducted with the micro-mirror will also be presented. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Estimation of triglyceride concentration is important for the health and food industries. Use of solid state biosensors like Electrolyte Insulator Semiconductor Capacitors (EISCAP) ensures ease in operation with good accuracy and sensitivity when compared to conventional sensors. In this paper we report on packaging of miniaturized EISCAP sensors on silicon. The packaging involves glass to silicon bonding using adhesive. Since this kind of packaging is done at room temperature, it cannot damage the thin dielectric layers on the silicon wafer unlike the high temperature anodic bonding technique and can be used for sensors with immobilized enzyme without denaturing the enzyme. The packaging also involves a teflon capping arrangement which helps in easy handling of the bio-analyte solutions. The capping solves two problems. Firstly, it helps in the immobilization process where it ensures the enzyme immobilization happens only on one pit and secondly it helps with easy transport of the bio-analyte into the sensor pit for measurements. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Measurement in liquid media is a major challenge in real-time detection using resonant cantilevers. This is addressed in the present study by fabricating sub-micron thick cantilevers followed by functionalization for biomolecule detection. The fabricated cantilever resonator beams of thickness 165 nm were used for measurements in two systems: (i) human immunoglobulin (HIgG) as the antibody on the cantilever sensing mouse immunoglobulin (MIgG) as corresponding antigen, and (ii) detection of triglyceride (TG) based on the enzymatic hydrolysis with lipase, using tributyrin as a model. In both cases, the beams were functionalized for covalent bonding of the protein receptor. The label-free detection was carried out by measuring the shift in resonance frequency at higher modes, using a laser Doppler vibrometer in liquid and in air. The calibration showed a linear correlation between the bioanalyte concentration and change in the resonance frequency. Notably, detection of antigen mass as low as 434 ± 59fg and triglyceride concentration in the nM range with limit of detection as 7 nM in liquid interface was achieved, greatly improving the sensitivity of bioanalyte detection in liquid samples. Although frequency-based methods are highly sensitive, the issues with measurement liquid medium limit their application. In the present report, these issues were addressed by fabricating sub-micron thick cantilever beam, choosing an appropriate functionalization method without affecting the sensitivity, and measurement at higher modes. These have resulted in circumventing issues like damping and hydrodynamic loading thus improving its potential as real-time sensor.

Suspended Gate Field Effect Transistor (SGFET) with lower subthreshold swing (S) can overcome high power dissipation during switching events. An electrostatic actuator, which is the fundamental building block of SGFET is fabricated using surface micromachining technique. Using a series feedback capacitor, the actuator was stabilized beyond the pull-in instability limit. The presence of negative differential capacitance is demonstrated by the voltage amplification method, which reduces the body factor (m) value less than 1.

We report the fabrication of potentiometric electrolyteinsulator capacitor (EISCAP) biosensors based on silicon and porous silicon (PS) substrates with oxide and stacked oxidenitride dielectrics. These biosensors have been calibrated for the detection and estimation of bioanalytes like tributyrin and urea, based on enzymatic reactions and have a linear detection range from 0.1 mM to 20 mM of the bioanalyte concentration. These improved sensitivity EISCAP sensors were used for the estimation of the total acid content in rancid butter, estimation of enzyme (Lipase) activity and to estimate total triglyceride levels in blood serum. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal-oxide-based resistive random access memory (RRAM) synaptic devices typically suffer from high variability and strongly nonlinear conductance change. In this work, we demonstrate a SiO $_\textit{x}$ -based synapse with low operating voltages, excellent uniformity in the switching operation, and analog tunability of conductance. The devices also exhibit linear and symmetric conductance update. We demonstrate that the enhanced uniformity and analog tunability can be attributed to an interfacial switching mechanism which can be controlled through careful optimization of the device operating conditions.

The readout electronics is developed for an Electrolyte Insulator Semiconductor capacitor (EISCAP) sensor. The sensor detects the presence of bioanalytes from changes in the pH of the electrolyte through shifts in the capacitance–voltage characteristics. An EISCAP relaxation oscillator is embedded in a successive approximation analog-to-digital conversion algorithm to give a digital readout of the pH of the test solution. Further, a compact readout system is developed and implemented in a Programmable System on Chip (PSoC®). A measurement protocol using the miniaturised EISCAP devices is described, incorporating calibration to account for sensor variations. Testing is done using blood serum samples to estimate the triglyceride concentration within the clinical range of 50 to 150 mg/dL and compared with results from standard clinical measurement techniques.

The original version of this article unfortunately contained some mistakes. There is an error in the hemodialysis buffer composition mentioned in Sect. 2: Materials and methods, Subsection 2.1 Materials (Page No.4, Line No. 22–25).