本研究為利用TSMC標準0.18μm 1P6M CMOS 製程平台中的電容上金屬層(CTM)開發一款創新且具備優異機電轉換性能的電容式換能器設計與製程平台，以因應近年來高速發展的智慧物聯網技術對晶片在無線通訊、訊號處理和續航的要求；此平台能大幅降低元件共振時的運動阻抗，並且讓元件能運作於更低的直流偏壓，因此預期能更有利於與後端電路整合，實現SOC架構的設計方式，以提升晶片的能源使用效率和降低雜散電容，本研究將此新型平台命名為金屬-絕緣體-金屬(MIM)平台。
由於CMOS製程平台中各層金屬與氧化層之間具備優良的蝕刻停止與選擇比特性，可以透過不同蝕刻方式方便地釋放懸浮結構，MIM平台的開發是奠基於本團隊先前在TSMC標準0.35μm和0.18μm CMOS 製程平台中利用內層鋁銅金屬層所研發的TiN-C電容式換能器設計平台，透過改良和設計獨特的後製程、蝕刻孔以實現等效電容間隙僅有125~140nm的電容式共振器；相比於先前等效電容間隙為400nm的TiN-C平台以及其他團隊所設計的電容式換能器製造工藝，本研究開發的MIM平台共振器在相同的振動頻率和結構下，運動阻抗(R_m)和直流偏壓上有顯著地降低；量測結果顯示當10µm*60µm大小的共振器約操作於約4MHz左右時，MIM平台元件在16V的偏壓下擁有3.3kΩ的優異運動阻抗表現；而TiN-C平台的共振器則為則需要接近60V的偏壓且運動阻抗仍有24.72kΩ，由此可見本研究所開發之MIM平台具備的優異性能以及與電路整合的優勢。

In this research work, a novel capacitive transducer design and fabrication platform, which is named metal-insulator-metal (MIM) platform, with excellent electromechanical coefficient will be developed by using the Capacitor-Top-Metal layer (CTM) in the TSMC standard 0.18μm 1P6M CMOS process platform. Devices on MIM platform will have lower motional impedance during resonance and will be able to operate under a lower bias voltage; thus, it is expected to be more suitable for integration with on-chip transistor circuits, and have a better opportunity to make SOC design into practice. With the integration of mechanical devices and circuits, it will make chips with higher energy efficiency and can reduce the parasitic capacitance, which makes it suitable to deal with the rising requirements for accurate wireless communication, signal processing, and long battery life in the rapid development of Artificial Intelligence of Things (AIoT).
Due to the excellent etching stop characteristics between the metal and oxide layers in CMOS process platform, we can easily release the suspended structure through different etching methods. The development of MIM platform is based on our previous experience of developing TiN-C capacitive resonator platform by using the internal aluminum copper metal layer in the TSMC standard 0.35μm and 0.18μm CMOS. By improving previous back-end process and designing unique etching holes, we have successfully achieved capacitive resonators with effective capacitive gap of only 125nm to 140nm on the proposed MIM platform. Compared with previous devices with capacitive gap of 400nm on TiN-C platform or other capacitive resonator fabrication processes designed by other research teams, the newly developed MIM platform enables devices with similar beam structures to have much lower motional impedance under the same resonant frequency, and significantly reducing the bias voltage. The measurement results show that when a resonator with a beam size of 10µm*60µm is operated near 4MHz, the one designed on MIM platform performs excellent motional impedance around 3.3kΩ under a bias voltage of 16V, while the one on the TiN-C platform has to be driven under a bias voltage of 60V and with motional impedance still near 24.72kΩ respectively. This shows the excellent performance improvement and circuit integration abilities of the proposed MIM platform.

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