Abstract
This paper introduces a thermoelectric-type sensor with a built-in heater as an alternative approach to the measurement of vacuum pressure based on frequency modulation. The proposed sensor is fabricated using the TSMC (Taiwan Semiconductor Manufacturing Company, Hsinchu, Taiwan) 0.35 μm complementary metal-oxide-semiconductor-microelectro-mechanical systems (CMOS–MEMS) process with thermocouples positioned central-symmetrically. The proposed frequency modulation technique involves locking the sensor output signal at a given frequency using a phase-lock-loop (PLL) amplifier to increase the signal-to-noise ratio (SNR) and thereby enhance the sensitivity of vacuum measurements. An improved first harmonic signal detection based on asymmetrical applied heating gives a precise measurement. Following calibration, the output voltage is in good agreement with the calibration values, resulting in an error of 0.25% under pressures between 0.1–10 Torr.
Highlights
Advances in micromachining and the miniaturization of electronic circuits has necessitated the development of ever smaller vacuum sensors [1,2]
A complementary metal-oxide-semiconductor (CMOS)–mechanical systems (MEMS) has proven effective in the development of SOC technology, due to the maturity of the processes and its compatibility with standard CMOS technology [3,4,5]
Thermal micro-sensors for the measurement of vacuum pressure have proven highly effective in terms of pressure range, accuracy, and reliability [6,7,8,9,10,11], and this in turn has prompted efforts to develop these devices using CMOS–MEMS technology to facilitate installation [12,13]
Summary
Advances in micromachining and the miniaturization of electronic circuits has necessitated the development of ever smaller vacuum sensors [1,2]. Thermopiles, based on the Seebeck effect, have been used for the monitoring of gas flow, vacuum pressure, and even as accelerometers [8,9,10,12,15]. These devices can be produced using batch-processing and researches have presented a broad range of commercial applications [10,18]. Gas conductance Gg under pressure P dominates the response of the proposed thermoelectric vacuum sensor described as follows: Gg(P). The measured signal is locked at frequency f, such that only the amplitude T1 is read from the PLL
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