The residual stress generated by thin-films processing influences the devices’ performance and reliability. In this work, an optical-based laser scan technique is used to evaluate the residual stress of thin films. The study focuses on the thin films, commonly used in micro-electromechanical systems (MEMS) device fabrication namely thermally grown silicon dioxide, low-pressure chemical vapour deposited (LPCVD) polysilicon, plasma-enhanced chemical vapour deposited (PECVD) silicon oxide and plasma-enhanced chemical vapour deposited (PECVD) silicon nitride. The radius of curvature (ROC) of the substrate and the thin film deposited substrate are measured using a 780 nm wavelength laser source. The change in ROC is then used to determine the film stress using Stoney’s equation. The input parameters in Stoney’s equation comprise the material properties and thickness of the substrate material, thickness of the film and change in ROC, and play a crucial role in deciding the accuracy of the stress value. In that regard, the material property of the silicon (100) substrate measured using the nanoindentation technique was found to be 222 GPa for 0.064 Poisson’s ratio. A different set of experiments was performed to accurately evaluate the thickness of the substrate, and thickness of thin films using surface profilometry. The residual stress obtained for thermally grown silicon dioxide (of 110 nm thickness) thin film was −327 MPa. The polysilicon thin film (of 500 nm thickness) deposited on the oxidized silicon substrate incorporates −122 MPa stress on the substrate. The silicon oxide thin film (of 450 nm thickness) and silicon nitride thin film (of 620 nm thickness) deposited using the PECVD technique were found to induce residual stress of −163 MPa and −632 MPa, respectively, on the substrate.

This research paper presents a comprehensive experimental investigation into the stress values of widely used thin films in micro-electro-mechanical systems (MEMS) devices. The study aims to provide valuable insights into the mechanical behaviour of these thin films, which is crucial for optimising the design and reliability of MEMS devices. The thin films under scrutiny include silicon oxide, silicon nitride, polysilicon thin films and composite stacks. A series of experiments was conducted to measure and analyse the inherent stresses present in these thin films. The experimental setup employed a state-of-the-art laser-based non-contact non-destructive technique to ensure precise and accurate stress measurements. Our findings reveal a nuanced understanding of the stress values exhibited by thin films under different growth conditions and fabrication processes. The impact of factors such as deposition techniques and film thickness on stress characteristics is also examined. The results provide crucial data for MEMS engineers and researchers striving to enhance the performance and reliability of microscale devices. Furthermore, this research contributes to the ongoing effort to establish a comprehensive database of thin-film stress values, aiding in the development of robust computational models for MEMS design. The implications of our findings extend to the optimization of fabrication processes, ultimately advancing the field of MEMS technology by addressing challenges related to mechanical reliability and structural integrity.

This paper presents the fabrication and characterization of a MEMS bulk micromachined piezoresistive accelerometer. For transduction of acceleration into output voltage, polysilicon piezoresistors are used. Due to cost effectiveness, polysilicon piezoresistors are preferred over SOI-based silicon piezoresistors. The accelerometer is designed using FEM-based MEMSCAD tool CoventorWare (R). The accelerometer sensor is realized using a hybrid approach, consisting of wet and dry bulk micromachining techniques. The developed sensor is characterized for static and dynamic performance using nano-indenter and electrodynamic shaker, respectively. From static characterization, stiffness and natural frequency are found to be 7.25 kN/m and 6.78 kHz, respectively. From dynamic characterization, bandwidth and sensitivity are found to be 475 Hz and 10 mV/V/g, respectively. (c) 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Advances in Nanomaterials and Devices for Energy and Environment.

This work demonstrates a MEMS piezoresistive pressure sensor and its interface circuit based on a versatile current conveyor based current signal processing. To exploit the effectiveness of current mode design in VLSI, the proposed interface electronics utilizes a differential current signal and performs trans-impedance conversion through a single-ended grounded gain resistor, thus ensuring high sensitivity and linearity. The current mode approach utilizes minimal active components with just two positive current conveyors (CCII+) in a closed loop architecture, thus eliminating the need for a negative current conveyor (CCII-) or an extra CCII+ to implement the same. This approach delivers linearity and offers ease of offset balancing through external control voltages, one each for incremental and decremental cancellation. The circuit performance is investigated in simulation using AD844, which represents a functional current conveyor. Further, the proposed interface is integrated with the fabricated MEMS piezoresistive pressure sensor to obtain a sensor-electronics module. Experimental evaluation of the module reveals a sensitivity of 13.7 V/Bar for low pressure input (0-100mBar).

In Micro-electro-mechanical Systems (MEMS) based pressure sensors and acoustic devices, deflection of a membrane is utilized for pressure or sound measurements. Due to advantages of capacitive pressure sensor over piezoresistive pressure sensors (low power consumption, less sensitive to temperature drift, higher dynamic range, high sensitivity), capacitive pressure sensors are the 2nd largest useable MEMS-based sensor after piezoresistive pressure sensors. We present a normal capacitive pressure sensor, for continuous sensing of normal and abnormal Intraocular Pressure (IOP). The composite membrane of the sensor is made of three materials, i.e., Si, SiO2 and Si3N4. The membrane deflection, capacitance variation, mechanical sensitivity, capacitive sensitivity and non-linearity are discussed in this work. Mathematical modeling is performed for analytical simulation, which is also compared with Finite Element Method (FEM) simulations. MATLAB is used for analytical simulations and CoventorWare is used for FEM simulations. The variation in analytical result of deflection in membrane w.r.t. FEM result is about 7.19%, and for capacitance, the variation is about 2.7% at maximum pressure of 8 kPa. The non-linearity is about 4.2492% for the proposed sensor for fabrication using surface micro-machining process.

A lot of work on clamped circular, square and rectangular shaped capacitive pressure sensor has been carried out. However, to the best of our knowledge, no elaborate work has been performed on mathematical formulation and simulation of clamped elliptical shaped capacitive pressure sensor in literature. This paper describes the mathematical modelling and simulation of normal mode clamped elliptical shaped capacitive pressure sensor. The study of various performance parameters like maximum diaphragm deflection, capacitance variation, mechanical sensitivity, capacitive sensitivity and non-linearity is also carried out for operating pressure range of 0kPa – 18 kPa. For circular capacitive pressure sensor, the operating pressure range is modified according to physical dimensions i.e. thickness and radius of diaphragm, separation gap between plates and maximum deflection. For same overlapping area between plates (10000 π mm 2 ), the comparison of elliptical shapes of different eccentricities with circular shape diaphragm is carried out. The thickness of diaphragm is taken as2 μm and separation gap is 1 μm in all the designs which are used in this work. In this comparative study, it is observed that elliptical shaped capacitive pressure sensors have better linearity than circular diaphragm pressure sensor.

Wet bulk micromachining of silicon is a convenient and economical method for realizing various silicon-based microsensors and actuators. Tetramethylammonium hydroxide (TMAH) based anisotropic wet etching is popular due to it being less toxic and CMOS compatible. The etch rate of TMAH depends on the wafer's crystal plane orientation and temperature/concentration of solution. While using TMAH to realize a pressure sensor diaphragm, the etching of {111} planes causes underetching, causing a deviation in the intended size of the diaphragm, inducing variation in the designed characteristics of the device. It is necessary to estimate and minimize these deviations. Experiments were designed and the rate of etching for (100) and (111) planes using 25 wt.% TMAH have been determined at different temperatures. Linear fit equations are obtained from experimental data to relate the underetch per unit depth to the solution temperature. These findings are extremely useful in the fabrication of silicon diaphragms with precise dimensions. While using anisotropic wet etchants to realize proof mass for accelerometers, the etchants attack the convex corners. This necessitates a suitable design of compensating structure while realizing microstructures with sharp convex corners. Experimental studies are carried out to protect convex corners from undercutting and the results are reported.

This study evaluates a family with two siblings having severe growth retardation and facial dysmorphism, born to consanguineous normal healthy parents. Affymetrix CytoScan 750K microarray showed a 34-Mb pericentric homozygous region on chromosome 6 for both siblings. CUL7 was one of the 141 genes present in this region. Sanger sequencing of CUL7 gene detected a 2-bp novel deletion in the 15th exon (c.2943_2944delCT of the cDNA). This deletion leads to a frameshift and a premature termination signal much upstream of the wild-type termination signal, leading to a nonsense mediated decay of the mRNA. CUL7 protein plays an important role in formation of 3M complex, ubiquitination, microtubule dynamics and cell cycle regulation. Mutations in CUL7 gene is known to cause a rare 3M syndrome. Information about the novel mutation has been accepted in the ClinVar database with rs1064792895.

Piezoresistive pressure sensors are one of the most important and oldest applications of microelectromechanical systems (MEMS). In this paper, a conventional piezoresistive pressure sensor has been simulated and thoroughly analyzed for is output characteristics using finite element method (FEM) tool COMSOL Multiphysics ® . The stress distribution and displacement on the surface of the diaphragm is ascertained and the positions of the piezoresistors are optimized in order to obtain the best possible sensitivity and the linearity of the piezoresistive pressure sensor. The goal in pressure sensor design is to obtain best possible sensitivity, without compromising on the linearity. This goal can be achieved by realizing some structures on the diaphragm, where the stresses are concentrated, namely stress concentration structures (SCS). In this work, a cross beam-membrane (CBM) structure has been taken as a case study for SCS. The conventional pressure sensor structure is compared with CBM structure in terms of sensitivity and linearity using FEM analysis and the results are reported.

This work describes the design and fabrication of a barometric pressure sensor for MAV application. The sensor has polysilicon piezoresistor and wet bulk micromachined diaphragm. The fabricated sensor shows good sensitivity of 34.78 mV/Bar at and an excellent non-linearity of <0.11

The paper presents Micro-electro-mechanical system (MEMS) based clamped circular capacitive pressure sensor with pre-stressed diaphragm made of polysilicon material with compressive residual stress. The residual stress affects the mechanical performance of material thereby influencing the performance of the device. The used polysilicon material is assumed to have a Young’s modulus of elasticity, Possion ratio and residual stress as 160GPa, 0.22 and −80 MPa, respectively. The simulations of diaphragm deflection (according to small deflection theory), capacitance variation with respect to pressure application and capacitive sensitivity for blood pressure sensing application has been carried out using MATLAB ® program and results have been presented. For simulation results, mathematical formulations have also been performed. The deflection, capacitance variation due to pressure application from 1.0 – 1.4 bar (blood pressure range) and sensitivity are obtained for various diaphragm thicknesses after optimization. In optimization, maximum possible diaphragm radius is obtained for a particular thickness of diaphragm, keeping small deflection theory of plates and pull-in under consideration.

The paper presents analytical modelling and Finite Element Method (FEM) based simulation of clamped circular capacitive pressure sensors for Intraocular Pressure (IOP) measurement. The parallel plate capacitive pressure sensor consists of a fixed backplate and a circular shaped clamped thin diaphragm made of silicon material. The plates are separated by a vacuum media. MATLAB® and COVENTORWARE® are used for analytical and FEM simulations, respectively, and a comparison of maximum deflection in the diaphragm, capacitance after pressure application and sensitivity is carried out. A pressure range of 0-60 mmHg is used for IOP measurement.

This paper presents the mathematical modeling-based design and simulation of normal mode MEMS capacitive pressure sensor for blood pressure sensing application. The normal blood pressure of human being is 120/80 mmHg. But this range varies in case of any stress, hypertension and some other health issues. Analytical simulation is implemented using MATLAB. Basically, normal mode capacitive pressure sensors have a fixed plate and a moveable diaphragm which deflects on application of pressure with the condition that it must not touch the fixed plate. Deflection depends on material as well as thickness, shape and size of diaphragm which can be of circular, elliptical, square or rectangular shape. In this paper, circular shape is chosen due to higher sensitivity compared to other diaphragm shapes. Deflection, base capacitance, change in capacitance after applying pressure and sensitivity are reported for systolic and diastolic blood pressure monitoring application, and study involves determining the optimized design for the sensor. Diaphragm deflection shows linear variation with applied pressure, which follows Hooks law. The variation in capacitance is logarithmic function of applied pressure, which is utilized for analytical simulation.

In this paper, we present a current mode interface design for full bridge MEMS piezoresistive pressure sensor utilizing a differential current signal with high sensitivity and linearity. MEMS-piezo resistive pressure sensors are popular as they are small, robust and low cost. Typical sensitivity of these sensors is of the order of few millivolts per Bar. The presented approach utilizes the current signal from the bridge output port and detects ultra-low variations in the sensor thus enhancing the sensitivity. The current mode approach uses two positive second-generation current conveyors (CCII+) in a closed loop fashion thus eliminating the use of negative current conveyor (CCII-). This approach conveys high common mode cancellation, ease of offset balancing, increased sensitivity and eliminates the use of the current source as excitation. The circuit performs trans-impedance conversion through a single ended gain resistance and eliminates the use of any further amplification stages. The performance of the interface design is evaluated in simulation using AD844 of analog devices which represents a functional current conveyor. Moreover, the results are evaluated with a MEMS pressure sensor and are characterized from 0 to 1000mBar using the interface circuit with an achieved sensitivity of 11.7V/Bar.

Piezoresistive pressure sensors are one of the most popular types of sensors used for pressure sensing. These sensors consist of a diaphragm and piezoresistors. The characteristics of the pressure sensor can be modelled using analytical expressions for thin plates and the theory of piezoresistance to obtain a quick guideline and estimation of critical parameters of pressure sensor such as linearity and sensitivity, before detailed finite element method analysis. In the present work, a MATLAB (R) based program has been developed for determining the deflection of diaphragm, x- and y-directed stresses of the diaphragm, the relative change in resistance at the piezoresistor locations and eventually the sensitivity and linearity of the sensor. Finally, the use of the program is demonstrated through a case study.

Micro cantilevers are an important component of smart sensors as they detect the stress on surfaces caused by various physical/chemical or biological parameters. The proper design of the cantilever dimension helps to achieve optimum sensitivity of sensor. This work presents the design simulations of Si cantilever beam using Finite element method. The design is implemented by fabrication of a pair of cantilevers on a single trench. Deep Reactive-Ion Etching (DRIE) was employed to release the Sicantilever from bulk silicon. The released structure was characterized by using Laser Doppler Vibrometer (LDV). The Eigen frequency of the cantilever measured by LDV is found to be similar to the designed specifications. The design and fabrication aspects have been discussed in the paper along with analysis of the Eigen frequency achieved.

Piezoresistive sensing is one of the most frequently used transduction mechanism in pressure sensors. The piezoresistor placement on the diaphragm and the piezoresistor configuration play a pivotal role in determining the output characteristics of a pressure sensor. In this work, two different pressure sensors with different transverse piezoresistor configurations are studied to determine the effect of piezoresistor configuration on the sensitivity and non-linearity of the pressure sensors. A sensor structure with a square diaphragm size of 1,480 µm edge length and diaphragm thickness of 50 µm is chosen for the study. The design considerations for piezoresistor placement and the piezoresistor shapes are discussed in detail. The sensors are fabricated with bulk micromachined diaphragm and polysilicon piezoresistors. The sensor characteristics are determined for three temperatures, namely, −5, 25 and 55 °C and for a pressure range of 0–30 Bar. The characterization results indicate that the design with two piezoresistor arms in transverse piezoresistor configuration (2 × 2 Design) has higher sensitivity than the single arm configuration (2 × 1 Design) by about 25 % at 25 °C but it also has a higher non-linearity. The study shows the importance of selecting the proper piezoresistor configuration in the design of pressure sensors.

In this work, the fabrication and characterization of eight different polysilicon piezoresistive pressure sensors are reported. The sensors are fabricated simultaneously by putting the different designs on the same mask set and the sensitivity and non-linearity characteristics are plotted. The output responses of the different sensors are reported at three temperatures (-5, 25 and 55 degrees C). Out of the eight sensors with different diaphragm sizes and piezoresistor configurations, the sensor with diaphragm edge length of 1,280 mu m and 2x1 configuration is found to have optimum characteristics, with good non-linearity and acceptable sensitivity. For this sensor, a sensitivity of 3.83-4.26 mV/Bar and non-linearity of <0.38 % are obtained in the pressure range of 0-30 Bar.

Pressure microsensors are very frequently used for applications encompassing a wide range of operating pressure ranges. However, it is possible to use the same pressure sensor for different operating ranges (in a limited range) with satisfactory performance. In this work, we report the possibility of using a single sensor for different pressure ranges. Operating the sensor at a lower pressure range not only offers flexibility of usage but also enhances output performance in terms of sensitivity and linearity. The concept is demonstrated using a pressure sensor with implanted polysilicon piezoresistors and bulk micromachined diaphragm fabricated using a standard process. The characterization data of the sensor is analyzed for three pressure ranges (10 Bar, 20 Bar and 30 Bar). The results show that modifying the full scale pressure of operation from 30 to 10 Bar increases the sensitivity from 6.03 mV/Bar to 6.58 mV/Bar. The non-linearity is also reduced by an order of magnitude from 3.89 % to 0.33 %.

This paper describes a comparative study of sensitivity and non-linearity of conventional and bossed diaphragm piezoresistive pressure sensor along with a performance enhanced design. The proposed structures take into consideration corner compensation to avoid distortion of the mesa structure during fabrication of bossed diaphragm structure using wet bulk micromachining. Optimum piezoresistors locations are calculated with the help of simulations carried out using finite element method (FEM) based tool COMSOL© Multiphysics. Since the sensitivity and non-linearity of conventional and bossed diaphragm structures showed a linear trend, empirical formulae are proposed using linear fit for quick and approximate calculation of sensitivity and non-linearity for a particular sensor structure. It is observed that high stress regions are also present near the boss - diaphragm interface and hence a design with piezoresistors placed at these regions is also proposed. This design is found to be enhancing the performance of piezoresistive pressure sensor compared to the conventional piezoresistor placement.