Rachit Sood | UMBC - Academia.edu (original) (raw)

Papers by Rachit Sood

Electroencephalogram (EEG) recording is a widely used method to measure electrical activity in th... more Electroencephalogram (EEG) recording is a widely used method to measure electrical activity in the brain. Rodent EEG brain recording not only is noninvasive but also has the advantages to accomplish full brain monitoring, compared with that of the invasive techniques like micro-electrode-arrays. In comparison to other noninvasive recording techniques, EEG is the only technique that can achieve sub-ms scale time resolution, which is essential to obtain causal relationship. In this work, we demonstrated a simple microfabrication process for developing a high-density polyimide-based rodent EEG recording cap. A 34-channel rodent electrode array with a total size of 11mmx8mm, individual electrode diameter 240µm and interconnect wire linewidth 35µm was designed and fabricated. For the fabrication process, we first deposit 350nm SiO2 on a silicon substrate. We then fabricate 6-7µm thick first layer polyimide caps with fingers and contact holes. Gold deposition and then lithography etching of 34 channel contact-electrodes and their interconnects were fabricated in the second step. The third step was to cover metal interconnects with a 10µm thick second layer polyimide, which was fabricated with photolithography before the final film released by HF undercutting etching of SiO2 layer. Then the fabricated EEG cap is interfaced with a commercial 34-channel female connector, which is soldered with 34-line wires. These wires are then connected to an ADC to record the EEG data in computer for post-processing. With polyimide, the EEG cap is biocompatible, and flexible which makes it suitable for good contact with rodent skulls.

Polarity is very important in developing materials with colossal dielectric. To meet the demands ... more Polarity is very important in developing materials with colossal dielectric. To meet the demands for the tunable devices and high dielectric parallel plate capacitors, several perovskites such as CaCu3Ti4O12 (CCTO), La2/3Cu3Ti4O12 (LCTO) Pr2/3Cu3Ti4 O12 (PCTO) and several other materials of this class have been studied all over the world. Detailed studies showed that results vary a lot based on processing methods, such as powder vs. multi crystals and single crystals. In spite of great progress in processing, low resistivity and process driven variables in properties remain a big hurdle for its applications as a dielectric capacitor. We observed that dielectric values are significantly changed when these materials are exposed to chemicals and biological agents. We used parallel plate capacitor design for making chemical and biological sensors from CCTO member of this group. The data indicated huge difference in the dielectric and resistivity of the exposed samples.

Crystals, Jan 5, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

ZnSe has been a great choice for the rare-earth and transition metal doping to develop lasers. It... more ZnSe has been a great choice for the rare-earth and transition metal doping to develop lasers. It is an excellent material for variety of optical applications due to wide transparency range, good fabricability and very low optical absorption similar to other selenides. NASA Marshall Space Flight Center has developed large crystals using physical vapor deposition (PVD) doped with transition metals for lasing. GaAs based quasi-phase matched structures have a lot of limitations including difficulty of frequency conversion from available high-power lasers. We are developing Si- and GaAs- based templates and using microfabrication process to deposit ZnSe using physical vapor transport (PVT) method. Experimental results of the fabrication of templates and growth of ZnSe on templates will be presented.

Smart Biomedical and Physiological Sensor Technology XVI

Conference on Lasers and Electro-Optics, 2020

We have fabricated GaAs motheye structures using contact photolithography printing. We have achie... more We have fabricated GaAs motheye structures using contact photolithography printing. We have achieved an average transmission improvement of 123% from 2000 cm -1 to 700 cm-1 (5 ¿urn-14 ¿urn) relative to an uncoated wafer.

Crystals, 2022

Chromium- and cobalt-doped zinc selenide nanoparticles were synthesized using a low-temperature r... more Chromium- and cobalt-doped zinc selenide nanoparticles were synthesized using a low-temperature reactive solution growth method. The morphological and optical characteristics were compared to those of doped zinc selenide (ZnSe) bulk crystals grown by the physical vapor transport (PVT) method. We observed agglomeration of particles; however, the thioglycerol capping agent has been shown to limit particle grain growth and agglomeration. This process enables doping by addition of chromium and cobalt salts in the solution. A slightly longer refluxing time was required to achieve cobalt doping as compared with chromium doping due to lower refluxing temperature. The nanoparticle growth process showed an average particle size of approximately 300 nm for both Cr- and Co-doped zinc selenide. The optical characterization of Co:ZnSe is ongoing; however, preliminary results showed a very high bandgap compared to that of pure ZnSe bulk crystal. Additionally, Co:ZnSe has an order of magnitude hig...

Quantum Sensing and Nano Electronics and Photonics XVII, 2020

Nano-arrays are an important structure for building chemical filters, photonic crystal waveguides... more Nano-arrays are an important structure for building chemical filters, photonic crystal waveguides, antireflection, or transmission devices. There are different methods of lithography to produce these nano-arrays, which include contact and projection photolithography, E-beam direct writing, and X-ray lithography. Contact photolithography is the most widely used method due to its simplicity and good for time and cost-saving. However, there are penalties that come with these benefits which include problems of generating Newton rings and difficulties of transferring patterns faithfully for situations at and beyond the diffraction limit. In this work, we fabricated nano-arrays for high power antireflection applications using contact photolithography. Fortunately for the antireflection application, pattern periodicity is more important than obtaining the exact shape of the nanostructure. The fabricated structure, even though not the same as the original pattern, can still produce promising antireflection results. We have studied how the range of the distance between the mask and the photoresist affects the shapes of the produced patterns including holes, posts, and cones. The experimental results with different shapes and periodic patterns produced by different diffraction distances are explained with simulation results involving Fourier transformation and Fresnel diffraction of the mask patterns.

Advanced Fabrication Technologies for Micro/Nano Optics and Photonics XIII, 2020

and telling us what having access to this work means to you and why it's important to you. Thank ... more and telling us what having access to this work means to you and why it's important to you. Thank you.

Smart Biomedical and Physiological Sensor Technology XVIII, 2021

Crystals, 2020

The effect of sulfur, iron, and chromium doping on the electrical characteristics of ZnSe single ... more The effect of sulfur, iron, and chromium doping on the electrical characteristics of ZnSe single crystals was studied. The crystals, grown by the physical vapor transport method (PVT) at NASA Marshall Space Flight Center, were characterized by measuring electrical resistivity, capacitance, and dielectric constant using LCR meter. The morphology was studied by scanning electron microscopy to determine the crystallinity and micro defects. The measured resistivity and dielectric constant showed tunability as the function of frequency in the range of 100 Hz to 100,000 Hz, indicating the suitability of doped material for tuning devices. Besides, for the range from 50 mV to 1000mV, there was no difference in values for the studied frequency range, indicating no degradation or breakdown in the material. All doped ZnSe crystals with sulfur, iron, and chromium showed a similar trend as the function of frequency. Cr-ZnSe showed very high resistivity and lower dielectric constant compared to S...