This paper presents design, fabrication and testing of a quad beam silicon piezoresistive Z-axis accelerometer with very low cross-axis sensitivity. The accelerometer device proposed in the present work consists of a thick proof mass supported by four thin beams (also called as flexures) that are connected to an outer supporting rim. Cross-axis sensitivity in piezoresistive accelerometers is an important issue particularly for high performance applications. In the present study, low cross-axis sensitivity is achieved by improving the device stability by placing the four flexures in line with the proof mass edges. Various modules of a finite element method based software called CoventorWare™ was used for design optimization. Based on the simulation results, a flexure thickness of 30 μm and a diffused resistor doping concentration of 5 × 10 18 atoms/cm 3 were fixed to achieve a high prime-axis sensitivity of 122 μV/Vg, low cross-axis sensitivity of 27 ppm and a relatively higher bandwidth of 2.89 kHz. The designed accelerometer was realized by a complementary metal oxide semiconductor compatible bulk micromachining process using a dual doped tetra methyl ammonium hydroxide etching solution. The fabricated accelerometer devices were tested up to 13 g static acceleration using a rate table. Test results of fabricated devices with 30 μm flexure thickness show an average prime axis sensitivity of 111 μV/Vg with very low cross-axis sensitivities of 0.652 and 0.688 μV/Vg along X-axis and Y-axis, respectively. © 2011 Springer-Verlag.

Ravi Sankar A

Electronics

School of Electronics Engineering

Chennai Campus

Jency J.G

Das S.

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Microsystem Technologies

In the past decade, micro/nano cantilever platforms have been actively explored for realizing variety of MEMS/NEMS sensor and actuator systems. In treatise, a majority of the cantilever platform based devices reported are non-monolithic structures with additional functional layers for improving their performance metrics. In this paper, for the first time, we elucidate the impact of an additional thin film Au layer which is typically used in the case of piezoresistive micro/nano cantilever surface stress sensors as a bio-interface for improving their chemical/biological selectivity and sensitivity. In this study, unlike the earlier reports in addition to the electro-mechanical response, we have also considered the phenomenon of thermal drift inaccuracy which has been seldom considered in the modeling and design stages of piezoresistive cantilever devices. The major component of inaccuracy i.e. multi-morph deflection induced due to the combined effect of multi-layered structure of a piezoresistive micro/nano cantilever sensor with a thin Au film and joule heating in the dc-biased piezoresistor is modeled and investigated. Here, the prime focuses are the following: (i) to investigate the effect of Au immobilization layer thickness and coverage on the thermo-electro-mechanical response and (ii) for a fixed sensor geometry, to identify an optimal Au immobilization layer thickness and coverage to nullify the multi-morph induced thermal drift. Premise has been investigated using a multi-physics modeling and simulation software in two phases. To validate the modeling approach, simulation results have been compared with experimental data reported in the literature. In phase-I, influence of the addition of Au immobilization layer on the sensor response is investigated. Results show that an addition of a 50 nm Au immobilization layer atop silicon monolithic structural layer with an integrated piezoresistor and a silicon dioxide isolation layer reduces resonant frequency by 15.23%, causes a change in multi-morph deflection by 2.83 times with a new behavior of reversal in cantilever bending direction and change in thermal sensitivity by 41.47%. In phase-II, impact of Au layer thickness and coverage on the sensor is analyzed. Results depict that apart from Au layer thickness, Au layer coverage area is also critical in governing the sensor response and by careful selection of the two parameters thermal drift component due to multi-morph deflection can be completely nullified. © 2019 IOP Publishing Ltd.

Materials Research Express

Influence of surface layer properties on the thermo-electro-mechanical characteristics of a MEMS/NEMS piezoresistive cantilever surface stress sensor

Over the last decade, surface stress-based piezoresistive cantilever biosensors have been extensively explored as a potential alternative for conventional clinical diagnostic techniques. The design of piezoresistive cantilever sensors is a complex multi-variable problem which involves the interplay between the thermal, electrical and mechanical design aspects of their constituent materials and geometry. Even though the literature includes examples where researchers have devised designs of piezoresistive cantilever biosensors, a majority of them have focused primarily on improving the electrical sensitivity by either dimensional optimization or material changes of their constituent layers. However, there are two important aspects of the sensor design which have been seldom addressed: (i) the negative impact of the transverse section of the U-shaped piezoresistor on the electrical sensitivity, and (ii) thermal drift in the output characteristics of the sensor. Although a few researchers have focused on the aforementioned factors, they have analysed them independently without considering their interdependence and cumulative impact on the sensor performance. In this paper, we devise a dual material multi-part U-shaped piezoresistor comprised of two p-type single crystalline silicon longitudinal sections and a p-type polysilicon transverse section. Evaluation of the proposed piezoresistor is performed in two stages using a finite element method-based numerical tool. In the first stage, the performance of the sensor with the multi-part piezoresistor is compared with the reported piezoresistors available in the literature. In the second stage, a comprehensive investigation of the multi-part piezoresistor is carried out to maximize the sensor performance. Results show that, compared to a conventional U-shaped piezoresistor, the proposed piezoresistor achieves improvement in the sensitivity ratio by 8.12 times. © 2018 IOP Publishing Ltd.

Journal of Micromechanics and Microengineering

Optimization of a nano-cantilever biosensor for reduced self-heating effects and improved performance metrics

Piezoresistive acceleration sensors have found a wide range of applications for the last four decades. However, in recent times, high performance piezoresistive acceleration sensors with lower footprint are in demand, especially in the fields of consumer electronics and biomedical engineering. The design of such sensors remains a challenging task due to the competing requirements of high electrical sensitivity (∆R/R) and resonant frequency (f0) along with low device footprint. In this paper, we elaborate the design and optimization of a highly miniaturized doubly clamped acceleration sensor with an integrated silicon nanowire as a piezoresistor. The diminutive size of the silicon nanowire helps in reducing the device foot print. The design is performed using two methods: (1) electrical approach and (2) mechanical approach. In the electrical approach, the conventional bulk silicon diffused piezoresistors are replaced with a silicon nanowire without changing the dimensions of the original structure. It is shown that compared to the conventional design, a silicon nanowire based sensor exhibits 2.51 times better performance in terms of electrical sensitivity. One of the major constraints with miniaturized high performance acceleration sensors is reduced resonant frequency. Therefore, in the mechanical approach we have devised a geometrical optimization technique to miniaturize the sensor geometry by keeping its resonant frequency constant. Numerical simulations are performed to validate the proposed miniaturized sensor with an integrated silicon nanowire as the piezoresistor. The sensor performance is evaluated with a new performance factor given as (ΔR/R)f02/Diesize, which takes into account the electrical sensitivity, the resonant frequency and the die size of the sensor. Results show that the proposed sensor design with an integrated silicon nanowire has 48.2 times better performance factor than a bulk piezoresistor based conventional acceleration sensor. © 2016, Springer-Verlag Berlin Heidelberg.

Design and optimization of a doubly clamped piezoresistive acceleration sensor with an integrated silicon nanowire piezoresistor

In recent times, catheters with integrated transducers have been extensively investigated in the field of biomedical engineering, especially for use in in vivo neonatal intensive care systems. An integral module of such systems is a blood pressure sensor that must fulfill the competing requirements of high sensitivity and small area. Typically, microelectromechanical systems-based membrane structures with integrated piezoresistors are used to realize such miniaturized blood pressure sensors. Conventionally, the electromechanical transduction of membrane deformation into an equivalent electrical signal is accomplished by piezoresistors connected in a fully active Wheatstone bridge configuration. However, such a configuration requires a large area for the placement of piezoresistors and layout of interconnects. Even though piezoresistors connected in a half-active Wheatstone bridge configuration overcome the area constraint, such an arrangement still suffers from reduced electrical sensitivity. In this paper we propose a novel three-terminal single-element piezoresistor membranebased miniaturized blood pressure sensor for less than 1 French catheter application. Design and optimization of the sensor is performed using numerical simulations to satisfy the competing requirements of high sensitivity, low structural non-linearity and high mechanical stability. Simulations are carried out to optimize the piezoresistor position, piezoresistor doping concentration and relative dimensions of the piezoresistor and the membrane. Results depict that sensor with a die size of 175×150×50 μm3 results in an electrical sensitivity of 14.03 μAA-1mmHg-1. Finally, a set of design guidelines are outlined for optimizing the performance of three-terminal piezoresistor-based blood pressure sensors. © 2017 IOP Publishing Ltd.

Biomedical Physics & Engineering Express

Design and optimization of a three-terminal piezoresistive pressure sensor for catheter based in vivo biomedical applications

In recent years, miniaturized piezoresistive pressure sensors have been extensively explored, especially for biomedical applications. Typically, the electromechanical transduction of a measurand into an equivalent electrical signal is accomplished by a fully active Wheatstone bridge (WSB). Even though, a fully active WSB has advantages in terms of improved sensitivity and noise cancellation, still it suffers from a major limitation in terms of area, especially for applications like cardiac catheters that demand ultra-miniaturized pressure sensors. Hence for miniaturized sensor design, half-active WSB or single element piezoresistor is deployed by various researchers. In this paper, performance of a single element piezoresistor (3TP-1) is compared with a half-active WSB configuration and other single element piezoresistors such as four terminal piezoresistor (4TP), multi-terminal piezoresistor (MTP) and another three terminal piezoresistor (3TP-2) for area constrained applications. Investigation of the 3TP-1 is carried out by using a finite element method (FEM) based numerical simulation tool IntelliSuite® (version 8.7). Simulation results show that compared to a half-active WSB, the 3TP-1 has 35% better performance in terms of output voltage. Furthermore, it is found that compared to other single element piezoresistors, the 3TP-1 is more suited for realizing ultra-miniaturized pressure sensors both in terms of area and performance. © 2017 Elsevier Ltd

Measurement

Performance comparison of a single element piezoresistor with a half-active Wheatstone bridge for miniaturized pressure sensors

Coupled effects of an electroplated gold layer and damper holes drilled by Electro Chemical Discharge Machining (ECDM) process on the performance improvement of a quad beam capacitive accelerometer is presented in this paper. A simple quad beam-proof mass configuration with its beams located symmetrically at the centre of all the edges of the proof mass and connected to an outer supporting frame is considered in the present study. For a fixed damping ratio, prime-axis sensitivity of the sensor is increased by the damper holes whereas an electroplated gold layer improves the prime-axis sensitivity, cross-axis sensitivity, and Brownian Noise Equivalent Acceleration (BNEA). Moreover, the increased weight of the proof mass due to an electroplated gold layer further reduces the damping of the device which in turn helps to increase the prime-axis sensitivity more. A new figure of merit called Performance Factor (PF), defined as the ratio of the product of the prime-axis sensitivity and resonant frequency to the cross-axis sensitivity at a fixed damping ratio of 0.7 is used as a quantitative index to evaluate the performance improvement caused by the coupled effects of gold electroplating and ECDM processes. Simulation results show that for a device with damper holes of 8 μm diameter and electroplated gold layer of dimensions 3,000 μm × 3,000 μm × 20 μm, the prime-axis sensitivity is increased by more than 500 times, rotational cross-axis sensitivity and BNEA are reduced by around 10 and 30%, respectively and the PF is improved by around 482 times at a fixed damping ratio of 0.7. © 2011 Springer-Verlag.

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Publisher	Data powered by TypesetSpringer Science and Business Media LLC
ISSN	0946-7076
Open Access	0