Performance enhancement of a silicon MEMS piezoresistive single axis accelerometer with electroplated gold on a proof mass

Abstract

Performance enhancement of a silicon MEMS piezoresistive single axis accelerometer with electroplated gold on a proof mass is presented in this paper. The fabricated accelerometer device consists of a heavy proof mass supported by four thin flexures. Boron-diffused piezoresistors located near the fixed ends of the flexures are used for sensing the developed stress and hence acceleration. Performance enhancement is achieved by electroplating a gold mass of 20 μm thickness on top of the proof mass. A commercially available sulfite-based solution TSG-250 TM was used for the electroplating process. Aluminum metal lines were used to form a Wheatstone bridge for signal pick-up. To avoid galvanic corrosion between two dissimilar metals having contact in an electrolyte, a shadow mask technique was used to selectively deposit a Cr/Au seed layer on an insulator atop the proof mass for subsequent electrodeposition. Bulk micromachining was performed using a 5% dual-doped TMAH solution. Fabricated devices with different electroplated gold areas were tested up to ±13 g acceleration. For electroplated gold dimensions of 2500 μm × 2500 μm × 20 μm on a proof mass, sensitivity along the Z-axis is increased by 21.8% as compared to the structure without gold. Off-axis sensitivities along the X-and Y-axes are reduced by 7.6% and 6.9%, respectively.

Fe-B-Nd-Nb metallic glass thin films for microelectromechanical systems

“…For MEMS, there has always been a demand for device performance improvement that has inspired a subsequent search for thin film materials with superior properties. [1][2][3][4][5][6][7][8][9][10] Recent research has shed light on metallic glass thin films, [11][12][13][14][15][16][17][18][19][20][21] whose outstanding mechanical properties such as high fracture toughness, high yield strength, and high elastic limits are expected to improve the lifetime and reliability of devices. In addition, flexible formability of the metallic glass thin films under viscous flow conditions in the temperature range between glass transition and crystallization, called the super cooled liquid region (SCLR), enables the creation of structures never constructed using conventional microfabrication processes.…”

Coupled effects of gold electroplating and electrochemical discharge machining processes on the performance improvement of a capacitive accelerometer

“…It is a three element sandwich structure which contains (i) top and bottom fixed glass plates with metal electrodes and micromachined holes and (ii) proof mass with electroplated gold layer at its top surface which acts as a central moving electrode. This configuration was used for sensing vector acceleration along all the 3 axes, because of its relatively lower torsional stiffness along X and Y axes as compared to other quad beam (Ravi Sankar et al 2009a) and eight beam structures (Xiao et al 2008;Sim et al 1998). However, in the present work, an electroplated gold layer atop the proof mass is added to the basic configuration in order to improve the prime-axis sensitivity, BNEA and quality factor.…”

“…Various sensing mechanisms like capacitive (Yazdi and Najafi 2000;Rudolf et al 1990;Farahani et al 2009;Bernstein et al 1999;Rödjegård et al 2005;Lee et al 2005;Tsuchiya and Funabashi 2004;Francis et al 2000;Lötters et al 1997Lötters et al , 1998Wang et al 2007), piezoresistive (Kal et al 2006;Ravi Sankar et al 2009a;Engesser et al 2009), piezoelectric (Tsai et al 2009), tunnelling (Liu et al 1998), etc. are used to convert input acceleration into an equivalent electrical quantity.…”

“…Because of the asymmetry, proof mass will rotate for applied acceleration along X and Y axes. Recently Ravi Sankar et al (2009a) proposed the use of an electroplated gold layer atop the proof mass to reduce the asymmetry and hence reduce the cross-axis sensitivity in piezoresistive accelerometers. In the case of capacitive accelerometers, in addition to improving the prime-axis sensitivity, cross-axis sensitivity, Brownian noise and quality factor (Yazdi and Najafi 2000), an electroplated gold layer will decrease the damping ratio also which is an attractive property.…”

Performance optimization and mechanical modeling of uniaxial piezoresistive microaccelerometers

“…During the last three decades various microaccelerometers have been investigated based on piezoresistive (Amarasinghe et al 2007;Sankar et al 2009), capacitance (Chae et al 2005), piezoelectric (Hindrichsen et al 2009), thermal (Dauderstädt et al 1998), tunneling (Liu and Kenny 2001), and optical (Lee and Cho 2004) sensing principles. Each approach has its own inherent advantages and drawbacks.…”