3-axis accelerometer and strain sensor readout MEMS-based capacitive sensors Juan Santana Richard van den Hoven Imec-Holst Centre The Netherlands Imec- Holst Centre1st MEMSCON Event - 07 October 2010, Bucharest

Overview Summary MEMS based charge sensing Accelerometers & Strain sensors Technical Specifications Programmable gain by timing control, sensitivity and accuracy read-out Low-power TSMC CMOS 0.25  m with operating voltage (3.0V) ±2 g input range, 1mg resolution High linearity (1%) Parasitics insensitive Applications Accelerometers, strain sensors for structural assessment, automotive and BAN, industrial and healthcare Imec- Holst Centre

1st MEMSCON Event - 07 October 2010, Bucharest Architecture Timing sequence Novel Technique Integration of multiple pulses Variable gain set by number of pulses Integrated noise proportional to √N Timing allows duty-cycle control Signal-to-noise ratio control Decouples sensor from amplifier Allows readout of wide range of sensors Accurate sin(x)/x suppresses artifacts Multiplexed output Imec- Holst Centre

1st MEMSCON Event - 07 October 2010, Bucharest ASIC 2mm Y-channel X-channel Z-channel 4mm Bias stage MUX+buffer +digital ESD System Level characteristics 3-channel architecture 1 Analog multiplexed buffered output 1 Analog non-multiplexed (X channel) Synchronization signals available Embedded filtering (sin(x)/x response) 1 Bias voltage (V DD ) and 1 clock Minimum capacitance ESD structures Imec- Holst Centre

1st MEMSCON Event - 07 October 2010, Bucharest Results Accelerometer Strain sensor Variable sensitivity ~N Integrated Noise ~√N Imec- Holst Centre

1st MEMSCON Event - 07 October 2010, Bucharest Benchmarking Parameter DenisonPaavola ISSCC2008 IMEC-NL Acceleration strain range ~±1g±2g±2.5g ±20,000µe Variable gain Supply voltage V1.0V3.0V Power1.5µW 15µW Noise Floor (accel.) 1mg/√Hz704µg/√Hz70µg/√Hz Non-linearity<1%---<1% (accelerometer) <0.6% (strain sensor) Bandwidth10Hz1Hz100Hz FOM F√(W/Hz) µW·µg/Hz 8.1× × Technology0.8µm CMOS0.25µm CMOS Area mm² c 2 mm² (active) 8 mm 2 Imec- Holst Centre State-of-the-art readout architectures

1st MEMSCON Event - 07 October 2010, Bucharest Conclusions Company Versatile architecture for MEMS-based capacitive sensors Cost effective design requires less external components Low Power Sampled output relaxes demands of following stages Embedded filtering Novel technique to control gain and SNR of the readout Can be extended to many other types of capacitive based sensors