(A) mass-sensitive microchemical sensor system using thin-film bulk acoustic resonators (TFBARs)

Abstract

New thermally driven (TD) TFBAR based microchemical sensor has been proposed to apply for a VOC monitoring system. The high frequency sensing scheme with low frequency read-out is achieved by mixing the sensing signal with the reference signal which is generated from the thermally elevated hot membrane based TFBAR. The fabricated sensor shows higher sensitivity than that of the previous technology based sensors like QCM, SAW, and cantilever. First, The bulk-micromachined AlN based TFBARs have been designed and fabricated. The highly (002) textured AlN thin films with low stress have a Rocking curve of 1.8˚, a surface roughness of 8 nm, and a columnar grain width of about 24 nm. The TFBARs have been successfully fabricated using the Si (100) bulk micromachining technology. The full two port measured results of S11 and S21 are well explained by the modified Butterworth Van Dyke equivalent circuit model. The range of resonant frequency is 1.7 GHz to 1.9 GHz. The ranges of bandwidth and Q factors are 50~70 MHz and 700 ~ 1500, respectively. Next, we have proposed and fabricated the TD TFBAR VCO which has the TD TFBAR with a microheater element as a resonator. The negative resistance for the oscillating circuit is achieved by using the capacitive feedback circuit scheme called as Colpitts type oscillator. A transistor, resistors for bias, capacitors with small capacitance, and an inductor with small inductance are implemented on an InGaP HBT MMIC. The bulk micromachined TD TFBAR with 20 μm width of microheating line is successfully fabricated. The membrane temperature is calculated using the temperature coefficient of resistance (TCR) of Mo heating line. The measured TCR of Mo is 0.237%/℃, and the temperature of a membrane in the condition of 2.5 V of Vheater is about 260℃. The area and the Q factor of the TFBAR are 200 × 200μ㎡ and 1400, respectively. The TD TFBAR VCO shows the output power of 6.5 dBm and the phase noise of -109 dBc/Hz at an off-set frequency of...