This paper presents fabrication and testing of a high performance quad beam silicon piezoresistive Z -axis accelerometer with a very-low cross-axis sensitivity. Cross-axis sensitivity in piezoresistive accelerometers, mainly caused by the asymmetric structural design is an important issue primarily for high performance applications. In the present study, symmetry of the structure is achieved by shifting the center of mass of the proof mass toward the beam plane by selectively electroplating a 20 μm thick gold layer atop the proof mass and simultaneously reducing the silicon thickness from backside of the proof mass surface. Silicon shadow mask technique was used to deposit a Cr/Au seed layer on the selected regions of the proof mass followed by an electroplating process to achieve the 20 μm thick gold layer. Theoretical analysis shows that for an in-plane acceleration, the rotation of the thickness reduced proof mass with the electroplated gold layer is reduced by 69% compared to the accelerometer device with normal all-silicon proof mass keeping the resonant frequency of both the structures nearly equal. The accelerometer device was realized by a bulk micromachining technique using a 5% dual doped tetra methyl ammonium hydroxide (TMAH) solution. A new figure of merit called the performance factor (PF) defined as the ratio of the product of the prime-axis sensitivity and the square of the resonant frequency to the maximum cross-axis sensitivity is used as a quantitative index to evaluate the fabricated sensors with already reported devices. Test results of a fabricated device with 30 μm flexure thickness show a very-low cross-axis sensitivity of 0.316 μV/Vg for an in-plane acceleration and a PF of around 2900 MHz 2 .

A very-low cross-axis sensitivity piezoresistive accelerometer with an electroplated gold layer atop a thickness reduced proof mass

System development and characterization of a low noise low offset SOI MEMS–CMOS PCB-integrated multi-chip ±4g piezoresistive accelerometer sensor comprising a coupled multi-bandwidth variable-gain amplifier block and a thermal sensitivity and offset compensation block is presented in this work. Custom design and fabrication has been carried out for both the SOI MEMS sensor and the analog front-end for high precision and operational reliability. The system is shown to have a scale factor of ∼4 mV/g and an output nonlinearity

A high precision SOI MEMS–CMOS ±4g piezoresistive accelerometer

This paper presents a high-G MEMS accelerometer (HGMA). HGMA employs our-beams and central-island mass silicon structure, which features a robust stability in shock environment. Theoretical analysis is conducted to investigate the influence of structure parameters on the Von Mises stress distribution, mechanical sensitivity and natural frequency. With consideration of smaller stress, higher mechanical sensitivity and natural frequency, the structure parameters are optimized and the theoretical sensitivity of HGMA is calculated as 0.488μV/g. Then, the optimized structure is analyzed with finite element analysis software, which shows a maximum stress of 23.19 MPa and a frequency response of 408.19 kHz when a 100 000 g shock is loaded. Finally, a processing flow is designed and the structure is fabricated. Hopkinson bar is utilized to calibrate HGMA sample, and shows an experimental sensitivity of 0.5611μV/g. Long-term static bias and temperature experiments are arranged to evaluate HGMA. Test results verify the presented theoretical analysis, processing flow, and experiment method, which are of great value for guiding the design, fabrication and calibration of other HGMAs.

Design, fabrication and calibration of a high-G MEMS accelerometer

The mechanical properties of tissue change significantly during the progression from healthy to malignant. Quantifying the mechanical properties of breast tissue within the tumor microenvironment can help to delineate benign from cancerous stages. In this work, we study high-grade invasive ductal carcinoma in comparison with their matched tumor adjacent areas, which exhibit benign morphology. Such paired tissue cores obtained from eight patients were indented using a MEMS-based piezoresistive microcantilever, which was positioned within pre-designated epithelial and stromal areas of the specimen. Field emission scanning electron microscopy studies on breast tissue cores were performed to understand the microstructural changes from benign to malignant. The normal epithelial tissues appeared compact and organized. The appearance of cancer regions, in comparison, not only revealed increased cellularity but also showed disorganization and increased fenestration. Using this technique, reliable discrimination between epithelial and stromal regions throughout both benign and cancerous breast tissue cores was obtained. The mechanical profiling generated using this method has the potential to be an objective, reproducible, and quantitative indicator for detecting and characterizing breast cancer.

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Mechanical phenotyping of breast cancer using MEMS: a method to demarcate benign and cancerous breast tissues.

Dielectric polymer nanocomposite materials with great energy density and efficiency look promising for a variety applications. This review presents the research on Poly (vinylidene fluoride) (PVDF) polymer and copolymer nanocomposites that are used in energy storage applications such as capacitors, supercapacitors, pulse power energy storage, electric vehicles, energy harvesting, etc. It mainly focuses on the electrical characteristics of the composite film materials with various types of filler. The electrical properties of the composite films have been explored including dielectric permittivity, dielectric loss, dielectric breakdown strength, energy density, and efficiency, as well as finite element analysis. Nanomaterials with surface modification can improve the electrical properties of the composites. Recently, compared to two-phase nanocomposites and three-phase nanocomposites, the multilayer nanocomposites with either combination of fillers and polymers aid to enhance electrical characteristics even more. The various materials used in supercapacitors are studied. It is observed that the usage of PVDF-based polymer composites in energy storage devices is very prospective, and future research into innovative polymer composites and ways to enhance their properties might be considerable. 

A review on polyvinylidene fluoride polymer based nanocomposites for energy storage applications

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 × 1018 atoms/cm3 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.

Design, fabrication and testing of a high performance silicon piezoresistive Z-axis accelerometer with proof mass-edge-aligned-flexures

This Letter presents simulation, fabrication and testing of a high-performance quad-beam silicon piezoresistive accelerometer with very low cross-axis sensitivity. Cross-axis sensitivity in piezoresistive accelerometers is an important issue particularly for high-performance applications. In the present Letter, low cross-axis sensitivity is achieved by improving the device stability by placing four flexures in line with the proof mass edges. The accelerometer device is realised in a single-step double-sided bulk micromachining technique using a 5% dual-doped tetra methyl ammonium hydroxide solution as an anisotropic etchant. Test results of four fabricated devices show an average prime-axis sensitivity of 559.5 µV/g/5 V, a maximum cross-axis sensitivity of 0.62% full scale (FS acceleration=13 g) of the prime-axis sensitivity and nonlinearity at a level of 0.5% of FS which are comparatively better than already reported devices and commercially available piezoresistive sensors.

Realisation of silicon piezoresistive accelerometer with proof mass-edge-aligned-flexures using wet anisotropic etching

This article presents the simulation and experimental validation of damping for an MEMS (micro-electromechanical systems) piezoresistive accelerometer with an optimized mass dimension and air gap. ...

Damping analysis of a quad beam MEMS piezoresistive accelerometer

An edge fed, dual band, quarter-wave transformer coupled, monopole, ultra-wideband (UWB), dodecagon-shaped miniaturized frequency reconfigurable antenna for ISM and wireless applications is designed, analysed and investigated. The impedance transformer is utilized in the structure for impedance matching and hence results in lower reflection coefficient values. The antenna uses defected ground structure (DGS) in the bottom and radiating patch that is practically loaded with three numbers of delta structures. The use of DGS reduces the value of gain and provides ultra-wideband bandwidth across the designed frequency. The addition of three delta structures in the patch improves the value of gain. Miniaturizing in the size of the antenna has been achieved by reducing the ground along the width that led to a total 30.41% size reduction in the fundamental circular patch antenna. The antenna exhibits two bands 1.82–3.61 GHz and 5.24–12.43 GHz thus antenna is suitable for ISM band, PCS, 5G, Wi-Fi/WiMAX/WLAN and other wireless applications. The fabricated antenna is frequency reconfigured by utilizing the switching property of four numbers of PIN diodes (BAP64-02V). Frequency reconfigurable antenna is used flexibly and versatile for various microwave applications based on the switching conditions (more than eight digital combination cases) of PIN diodes. The prototype measured results provide good agreements with the simulated reflection coefficients values in some mode of operations. Antenna radiating patch and ground is etched on FR-4 substrate of dimension 52 mm × 59 mm × 1.6 mm using printed circuit board technology. 

Dodecagon-Shaped Frequency Reconfigurable Antenna Practically Loaded with 3-Delta Structures for ISM Band and Wireless Applications

Stretchable energy storage materials are considered as essential component of fully stretchable and flexible electronics devices. Among the various stretchable/flexible electronic device and flexible super-capacitors are considered good because its power density is high, and it's long lasting, durable and safe. Super-capacitors have drawn more attention because they have a high capacity to store energy because it can deliver high peak current and store large amount of energy in less time with very less power loss. The present work the fabrication and characteristics of ultra-flexible super capacitor based on VLSI technology. The super-capacitor consist of PVdf(Poly Vinyledene Fluoride) unit it acts both substrate well as dielectric and gold as electrode. We have made a characterization of the fabricated ultra-flexible super-capacitor which exhibited high capacitance using impedance analyzer. We also analyzed the charging and discharging value of the super capacitor using cyclic voltammetry. Using PVdf as both substrate and dielectric the super-capacitor is made more economical.

J. Grace Jency

Papers

Design, fabrication and testing of a high performance silicon piezoresistive Z-axis accelerometer with proof mass-edge-aligned-flexures

Realisation of silicon piezoresistive accelerometer with proof mass-edge-aligned-flexures using wet anisotropic etching

Damping analysis of a quad beam MEMS piezoresistive accelerometer

Dodecagon-Shaped Frequency Reconfigurable Antenna Practically Loaded with 3-Delta Structures for ISM Band and Wireless Applications

Fabrication of ultra flexible super capacitor using polyvinylidene fluoride