A. Selvakumar

University of Michigan, Ann Arbor, MI, United States

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Publications (9)6.05 Total impact

  • A. Selvakumar, K. Najafi
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    ABSTRACT: A vertical actuator fabricated using a trench-refilled-with-polysilicon (TRiPs) process technology and employing an array of vertical oriented comb electrodes is presented. This actuator structure provides a linear drive to deflection characteristic and a large throw capability which are key features in many sensors, actuators and micromechanisms. The actuation principle and relevant theory is developed, including FastCap simulations for theoretical verification. Design simplifications have been suggested that enable one to use parallel plate analytical expressions which match simulation results with ∼5.6% error. Several actuators were designed and fabricated using the 7-mask TRiPs technology with calculated drive voltages as low as 45 V producing 10 μm of deflection. The actuators employed a mechanical structure that was 18 μm tall using a polysilicon layer 1.5 μm thick and occupying a total area of 750 μm by 750 μm. The actuators were successfully tested electrostatically and several microns of deflection were observed.
    Journal of Microelectromechanical Systems 09/2003; · 2.13 Impact Factor
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    Arjun Selvakumar, Navid Yazdi, Khalil Najafi
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    ABSTRACT: This paper presents a complete threshold acceleration detection microsystem comprising an array of threshold accelerometers and a low power interface circuit. The sensors were designed and fabricated using the bulk-silicon dissolved-wafer process. The process offers a wide latitude in sensor threshold levels, as demonstrated in the fabrication of devices with levels of 1.5-1000 g, bandwidths of 45 Hz to 40 kHz, with mass sizes ranging from 0.015 µg to 0.7 µg, and low-resistance gold-gold contacts for the switch. The interface circuit dissipates less than 300 µW, measures 2.2 mm×2.2 mm; it was fabricated in-house using a standard 3 µm, p-well CMOS (complementary metal oxide semiconductor) process, and is connected to the sensor chip in a multi-chip module. The key aspects of the microsystem are the implementation of sensor redundancy and supporting circuit logic to improve detection accuracy and fault tolerance, which are crucial factors in many applications. In addition, the microsystem supports communication with a standard microcontroller bus in a smart sensor network. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/49029/2/jm1206.pdf
    Journal of Micromechanics and Microengineering 01/2001; · 1.79 Impact Factor
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    A. Selvakumar, K. Najafi
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    ABSTRACT: This paper presents a new z-axis high-sensitivity silicon-micromachined capacitive accelerometer fabricated using a three-mask dissolved-wafer process (DWP). It employs capacitive sensing using overlap-area variations between comb electrodes and a torsional suspension system to provide high sensitivity without compromising bandwidth, full-scale range, or the pull-in voltage ceiling. Excellent electrical sensitivity is obtained by using high-aspect-ratio comb fingers with narrow air gaps of 2 μm and a large overlap area of 12 μm ×300 μm. Torsional suspension beams 150 μm long with a cross-sectional area of 12 μm ×3 μm are used to improve the mechanical gain. Simulations of the capacitance between sense fingers show a highly linear region over a wide 14-μm tip deflection range. Accelerometers were fabricated and yielded sensitivities of 263-300 mV/g, a nonlinearity less than 0.2% over a range of -4 to +3 g, a full-scale range of -4 to +6 g, and pull-in voltages greater than 8 V. A 3 dB cutoff frequency of 35 Hz was measured in air. The calculated thermomechanical noise in the sensor is 0.28 mg over this bandwidth
    Journal of Microelectromechanical Systems 07/1998; · 2.13 Impact Factor
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    A. Selvakumar, F. Ayazi, K. Najafi
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    ABSTRACT: This paper presents a high sensitivity silicon micromachined capacitive accelerometer fabricated using a three mask, dissolved wafer process. High electrical sensitivity is obtained by using high aspect-ratio comb fingers with narrow air gaps of 2 μm and large overlap area of 12 μm×300 μm. Torsional suspension beams 150 μm long with a cross-sectional area of 12 μm×3 μm are used to improve the mechanical gain (form factor). By using a varying overlap area method, the dynamic range, the pull-in voltage and the bandwidth are improved. The fabricated accelerometers yielded sensitivities of 263-300 mV/g, a nonlinearity less than 0.2% over a range of -4 g to +3 g, a full scale range of -4 g to +6 g and pull-in voltages greater than 8 V. A 3-dB cut-off frequency of 30 Hz was measured in air. The minimum resolution measured by the readout electronics was 0.077 g.
    Electron Devices Meeting, 1996., International; 01/1997
  • A. Selvakumar, N. Yazdi, K. Najafi
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    ABSTRACT: A complete threshold acceleration detection system is presented in this paper, possessing (i) an array of threshold accelerometers, and (ii) a low power interface circuit. The sensors were designed and fabricated using a modified bulk silicon dissolved wafer process. This process offers a wide latitude in sensor threshold levels, as demonstrated in the fabrication of devices, with levels of 1.5 g to 1000 g, bandwidth of 45 Hz to 40 kHz, with mass sizes ranging from 15 programs to 0.7 μgrams, and low-resistance gold-gold contacts for the switch. The interface circuit is fabricated in-house, using a standard 3 μm, p-well CMOS process and connected to the sensor chip, in a multi-chip module. Additionally, the system employs redundancy, to improve detection accuracy and fault tolerance, which is crucial in many applications. The system also supports communication with a standard microcontroller bus, in a smart sensor environment
    Micro Electro Mechanical Systems, 1996, MEMS '96, Proceedings. 'An Investigation of Micro Structures, Sensors, Actuators, Machines and Systems'. IEEE, The Ninth Annual International Workshop on; 03/1996
  • A. Selvakumar, K. Najafi, W.H. Juan, S. Pang
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    ABSTRACT: Not Available
    Micro Electro Mechanical Systems, 1995, MEMS '95, Proceedings. IEEE; 01/1995
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    ABSTRACT: A novel approach for excitation and detection of micromechanical structures is presented, which makes use of base drive. Test samples for translating base drive make use of piezoelectric excitation and detection, while test samples for bending base drive make use of thermal excitation and piezoresistive detection. Both alternatives are modeled and tested
    Solid-State Sensor and Actuator Workshop, 1992. 5th Technical Digest., IEEE; 07/1992
  • A. Selvakumar, N. Yazdi, K. Najafi
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    ABSTRACT: A novel approach of thermal excitation is presented, where thin micromechanical structures are suspended by deep-diffusion bases. Cantilevers and microbridges are fabricated, modeled and tested. Resonance frequencies are solely determined by the thin parts of the structures, and are independent of material properties and dimensions of the base. The efficiency for the amplitude of vibration is independent of the thickness and length of the base. Therefore short and thick bases can be applied, leading to relatively small temperature elevations inherent to thermal excitation.
    Sensors and Actuators A: Physical.