In this paper, we describe how magnetoresistive sensors can be integrated with microelectromechanical systems (MEMS) devices enabling the mechanical modulation of DC or low frequency external magnetic fields to high frequencies using MEMS structures incorporating magnetic flux guides. In such a hybrid architecture, lower detectivities are expected when compared with those obtained for individual sensors. This particularity results from the change of sensor’s operating point to frequencies above the 1/f noise knee.

https://www.mdpi.com/2072-666X/7/5/88/pdf

Hybrid Integration of Magnetoresistive Sensors with MEMS as a Strategy to Detect Ultra-Low Magnetic Fields.

Grayscale lithography is one area of lithography that has been relatively underutilized. There are several reasons for this, but one of the most prominent is the difficulty of modern techniques of grayscale exposure. However, this paper discusses a relatively novel approach to grayscale exposure using mask writing technology. Traditional lithography is characterized by the binary exposure of photoresist: meaning that some areas are exposed while other areas remain completely unexposed. The goal of grayscale lithography is to expose a gradient of intensities to photoresist. The result of this is a topography of photoresist that is potentially much more complicated than its binary counterpart. This paper will discuss direct write grayscale lithography using the Heidelberg DWL 66FS Laser Pattern Generator. Traditionally the Heidelberg DWL 66FS is used for binary exposure, but it also has the ability to vary laser intensity during an exposure. By varying the intensity of the focused laser beam, the user is able to expose photoresist differently in various regions of the substrate, generating the grayscale structure.

Maskless Direct Write Grayscale Lithography for MEMS Applications

A D-band waveguide diplexer, implemented by silicon micromachining using releasable filling structure (RFS) technique to obtain high-precision geometries, is presented here for the first time. Prototype devices using this RFS technique are compared with devices using the conventional microfabrication process. The RFS technique allows etching large waveguide structures with nearly 90° sidewall angles for the 400- $\mu \text{m}$ -tall waveguides. The diplexer consists of two direct-coupled cavity six-pole bandpass filters, with the lower and the upper band at 130–134 and 141–148.5 GHz, respectively. The measured insertion loss of the two bands is 1.2 and 0.8 dB, respectively, and the measured return loss is 20 and 18 dB, respectively, across 85% of the passbands. The worst case adjacent channel rejection is better than 59 dB. The unloaded quality factors of a single cavity resonator are estimated from the measurements to reach 1400. Furthermore, for the RFS-based micromachined diplexer, an excellent agreement between measured and simulated data was observed, with a center frequency shift of only 0.8% and a bandwidth deviation of only 8%. In contrast to that, for the conventionally micromachined diplexer of this high complexity, the filter poles are not well controllable, resulting in a large center frequency shift of 3.5%, a huge bandwidth expanding of over 60%, a poor return loss of 6 and 10 dB for the lower and the upper band, respectively, and an adjacent channel rejection of only 22 dB.

/pdf/silicon-micromachined-d-band-diplexer-using-releasable-3zke8kpdhf.pdf

Silicon Micromachined D-Band Diplexer Using Releasable Filling Structure Technique

Al mask combined with DRIE, which was etched by IBE and conventional RIE, were used to fabricate silicon micro-trench structures with high aspect ratio (HAR) for MEMS capacitors application. And the effects of IBE and RIE on mask and further on HAR structures are discussed. For Al mask, IBE produces smooth profile while RIE induces irregular breaches at the opening edge. For HAR structures, the sample affected by IBE shows less critical dimensional loss, lower sidewall roughness, and higher aspect ratio than that by RIE. Origin of these phenomena is that RIE is dominated by chemical reaction and aided by physical sputtering, and shows isotropy trendy, while IBE which is performed by pure physical sputtering exhibits anisotropy. In addition, etch rate shows a linear dependence on well-controlled process parameters and is uniform in IBE; in contrary, it shows coupling of uncertain variables and induces nonlinear performance in RIE. Consequently, the HAR trench structures with the average width of 5.98 μm, the aspect ratio of 24.4, and the verticality of 1.17 μm have been successfully fabricated by the synergetic effects of IBE and DRIE.

Fabrication of high aspect ratio silicon micro-structures based on aluminum mask patterned by IBE and RIE processing

Si-based MEMS resonant sensor: A review from microfabrication perspective

A systematic study of DRIE process for high aspect ratio microstructuring

In this paper four meander Serpentine flexures based movable beam structure has been used for design and development of capacitive contact RF MEMS switch for high frequency and space application. The developed MEMS switch is design on silicon wafer having the high resistivity ($\rho \gt 8 k\omega-cm$), high dielectric constant ($\varepsilon_{\mathbf{r}}= 11.8$) and low loss tangent ($tan\delta=0.001$,). Meander techniques are used to achieve the low pull-in voltage. The simulated value of pull-in voltage for four meander beam is 2.5 V for initial air height of 2.5 $\mu {\mathrm {m}}$. The developed switch exhibits the simulated RF parameters i.e. Insertion loss in Upstate (S21), return loss (S11), and Isolation (S21) are greater than 0.2, 20, and 30 dB respectively, across the complete frequency range (DC-40 GHz). The Method of Moments based ADS (advanced design system) and Finite element Method based coventorware and ANSYS HFSS full-wave simulator has been used for electromagnetic and electromechanical analysis of the 3D structure. The simulated Figure of merit (ratio of down state capacitance to up state capacitance) of the proposed switch is greater than 85. Further, The Simulated RF data are validated with equivalent circuit modal data over the entire frequency range.

Design and Simulation of RF MEMS Switch using Uniform Serpentine Flexure Four Meander Type Beam

The present work analyses the fundamental transport property of photogenerated carriers named low field mobility for Al0.5Ga0.5N/AlN/Sapphire-based MSM detector using five conventional mobility models. Using Atlas- Silvaco TCAD simulator, appropriate mobility models for differently doped structures were investigated for the least dark current density and improved photocurrent. For each doping case, low electric field mobility models have been compared for I-V characteristics, conduction current density, recombination rate, velocity and mobility of charge carriers. Since there are uncertainties for the most fundamental transport property like field-dependant mobility, therefore more study is required to model mobility for high performance of Wide Band Gap materials. In this work, the mobilities of carriers (mup and mun values) are not specified manually in the Silvaco simulation program however mobility model has been defined. The present work analyses various mobility models on dark current density, photocurrent, mobility and velocity of charge carriers in a photo-absorbent layer. Earlier experimental and theoretical studies have proved that variation in dark current density is greatly affected by doping concentration, structural dimension parameters and optical and electrical properties of detector’s materials. The main objective of the present work is selecting the suitable mobility model to get high Conduction current density in light to Conduction current density in dark ratio for each doping case. We also found that selection of models has a significant impact on spectral response. This simulation work could help align theoretical performance with experimental data and utilising AlGaN MSM detectors in modern UV detection and low noise applications. 

Manish Kumar Hooda

Papers

A systematic study of DRIE process for high aspect ratio microstructuring

Design and Simulation of RF MEMS Switch using Uniform Serpentine Flexure Four Meander Type Beam

Studying the effect of mobility models using TCAD simulation on the performance of AlGaN/AlN metal semiconductor metal metector

Investigation of CMOS compatible titanium nitride-based microheater for microthrusters

Electrical performance analysis of Al_0.5Ga_0.5 N/AlN/Sapphire-based MSM UV detector for high photocurrent