Conference Paper

3D Ultrasonic Gesture Recognition

DOI: 10.1109/ISSCC.2014.6757403 Conference: International Solid State Circuits Conference

ABSTRACT

Optical 3D imagers for gesture recognition suffer from large size and high power consumption. Their performance depends on ambient illumination and they generally cannot operate in sunlight. These factors have prevented widespread adoption of gesture interfaces in energy- and volume-limited environments such as tablets and smartphones. Wearable mobile devices, too small to incorporate a touchscreen more than a few fingers wide, would benefit from a small, low-power gestural interface. Gesture recognition using sound is an attractive alternative to overcome these difficulties due to the potential for chip-scale size, low power consumption, and ambient light insensitivity. Using pulse-echo time-of-flight, MEMS ultrasonic rangers work over distances of up to a meter and achieve sub-mm ranging accuracy [1,2]. Using a 2-dimensional array of transducers, objects can be localized in 3 dimensions.

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    • "Micromachined ultrasonic transducers (MUTs) have recently gained much interest and been developed for applications such as medical imaging [1] [2], gesture recognition [3], ultrasonic fingerprint sensors [4] and others. Unlike conventional ultrasonic transducers whose acoustic impedance is defined by the transducer's material properties, MUTs have a compliant thin membrane structure operating in a flexural vibration mode with acoustic impedance that can be wellmatched to a surrounding environment. "
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    ABSTRACT: This letter presents the novel CMOS-compatible all-metal-nitride resistive random access memory (RRAM) devices based on the TiN/AlN/TiN stack. The device has low operation current <;100 μA, retention of > 3×105 s at 150 °C, and ac endurance of up to 105 Hz. The device switch characteristics are found to agree with the filamentary switch mechanism. In addition, the RRAM devices built with an additional hafnium nitride capping layer have showed less switch voltage variations and stable switch characteristics.
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    ABSTRACT: A process to make self-curved diaphragms by engineering residual stress in thin films has been developed to construct highly responsive piezoelectric micromachined ultrasonic transducers (pMUT). This process enables high device fill-factor for better than 95% area utilization with controlled formation of curved membranes. The placement of a 0.65 μm-thick, low stress silicon nitride (SiN) film with 650 MPa of tensile residual stress and a low temperature oxide (LTO) film with 180 MPa of compressive stress sitting on top of a 4 μm-thick silicon film has resulted in the desirable self-curved diaphragms. A curved pMUT with 200 μm in nominal radius, 2 μm-thick aluminum nitride (AlN) piezoelectric layer, and 50% SiN coverage has resulted in a 2.7 μm deflection at the center and resonance at 647 kHz. Low frequency and resonant deformation responses of 0.58 nm/V and 40nm/V at the center of the diaphragm have been measured, respectively. This process enables foundry-compatible CMOS process and potentially large fill-factor for pMUT applications.
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