A CMOS-MEMS Capacitive Tactile Sensor For Non-Invasive Blood Flow Monitoring

本研究嘗試開發一種可應用於體外非侵入式血液流感測器，該感測器為電容式感測器主要利用結構間電極的形變，量測結構的電容變化，取得施加在感應器上的壓力變化。感測器以CMOS製程製作完成晶片的主體結構，再配合自行研發的後製程完成感測電容結構，以TSMC 0.35μm 2P4M製程為基礎加上MEMS後製程完成，其中使用兩層金屬M3以及M1作為犧牲層，另外兩層金屬M4還有M2 以及底部的導電多晶矽層組成三層共兩對感應電極，形成上、下兩組垂直的感應電容結構。本研究提出利用這兩組感應電容，再配合後端電容連結組態可以增加電容的變化，有助於提昇壓力感測的敏感度。研究中為了針對不同的量測壓力目標範圍，設計兩種不同的結構使其具有不同的彈性勁度，分別為L形以及方形設計，兩者的感測範圍為50mmHg 以及 200mmHg，配合後端的振盪器電路量測得兩者最大的頻率對壓力敏感度為0.1723 Hz/mmHg 以及 0.588 Hz/mmHg。In this research, we try to develop a capacitive tactile sensor for non-invasive blood flow monitoring. The capacitance variation of the capacitive tactile sensor was measured with the membrane deflection by an external pressure. This capacitive sensor is realized by using the CMOS-MEMS fabrication process which is based on TSMC 0.35μm 2P4M (2 polycrystalline silicon and 4 metal) process and self-developed post process. Two metal sacrificial layers of M1 and M3 are etched so the sensing electrodes of other two metal layers of M2, M4, and one polycrystalline silicon layer were formed. Two sensing capacitors consisting of three parallel sensing electrodes were connected vertically. The sensitivity of the sensor can be enhanced by a specific configuration of two sensing capacitors. Two different structure designs were proposed to cope with different sensing ranges. The detection range of L-type design is from 0 to 50 mmHg while the Square-type design is from 0 to 200 mmHg. The capacitance variation was recorded via an oscillator circuit converting a capacitance change into a frequency change. The maximum sensitivity of two designs are 0.1723 Hz/mmHg and 0.588 Hz/mmHg