Research On MEMS Microwave Frequency Detectors Based On MEMS Microwave Power Sensing Technology

Frequency is one of the three parameters (power, frequency and phase) for the microwave signal. Frequency detectors are widely used in various fields including military, aviation and communication. However, the existing frequency detectors have lots of disadvantages such as complicated system, high cost and low reliability. Above all, the fabrication of these detectors can not be compatible with mainstream Si or GaAs process. In order to solve these problems, novel MEMS microwave frequency detectors are researched based on the thermoelectric MEMS microwave power sensor and the capacitive MEMS microwave power sensor. The main works and the innovations are described as follows:(1) In terms of model, temperature and humidity effect, and frequency compensation of the thermoelectric MEMS microwave power sensorThe 2D model of the thermoelectric MEMS microwave power sensor is established to describe the temperature distribution based on the Fourier heat transfer equation. The relative error between the model and the simulation by ANSYS software has been reduced from 20% to 10%. The experiments demonstrate that the sensitivity of the power sensor is 0.26mV/mW, which is close to the result from the 2D model. In addition, the power sensor is packaged and put into the chamber. The temperature and humidity effect is tested and the temperature model is established. The measured results show that the output voltage increases with the surrounding temperature and the slop is close to 0.15mV/K at lOGHz. The voltage does not change with the humidity because the loaded resistors, GaAs substrate and the thermoples are insensitive to the humidity. Moreover, in order to make the sensitivity stable, a frequency-compensation type power sensor is proposed. The measured return loss is less than -26dB at 1-20GHz. For the incident power of 100mW, the output voltage after compensation does not change with the frequency of the signal and stands at 10.9mV. The innovations is that the 2D model of the the thermoelectric power sensor reduce the relative error with the measurements and explain the physical behavior of the electricity-heat-electricity conversion. The research on the temperature and humidity effect provides a experimental and theoretical method for the reliability of the thermoelectric power sensor, which will lay the foundation for its application in microwave signal detecting systems. The proposed frequency-compensation type power sensor overcomes the shortcomings of changing sensitivity.(2) In terms of model and intermodulation distortion of the capacitive MEMS microwave power sensorBased on mechanical theory,1-D model of the capacitive power sensor is established and the fabricated power sensor is tested. The measured return loss is less than -25dB and the insertion is about 0.1dB over X-band. The power experiments show that the sensitivity is close to 6.16aF/mW@8GHz,6.27aF/mW@10GHz and 6.03aF/mW@12GHz, which is clsoe to (he calculation of 6.44aF/mW from the model. On this basis, the intermodulation distortion of capacitive power sensor is also tested and the experiments show the third order intermodulation distortion is small when the frequency difference of two signals is more than 200kHz. The innovations is that the proposed 1-D model of the capacitive power sensor shows the relation among the displacement of the cantilever beam, capacitance change and the microwave power, which explains the physical behavior of the electricity-force-electricity conversion. The research of the third order intermodulation distortion breaks through the barrier of non-linear distortion in traditional power sensors based on diodes.(3) In terms of dynamic range of MEMS microwave power sensorsA cascaded MEMS microwave power sensor consisted of coupling-type power sensor and thermoelectric power sensor is proposed for high dynamic application. The experments domenstrates taht when the incident power increases from 1mW to 100mW, the thermoelectric power sensor works and the sensitivity is close to 0.088mV/mW@10GHz. When the incident power increases from 100mW to 150mW, the coupling-type power sensor works and the measured sensitivity is 8.6μV/mW@10GHz. On this basis, the microwave performance of this power sensor is optimized by impedance compensation technology. The experiments show the return loss is about -26dB over X-band while it is only -22dB without impedance compensation. The innovations is that the proposed cascaded power sensor extends the dynamic range for power detection. It also breaks through the barrier of degraded linearity of thermoelectric power sensor for high power and small sensitivity of coupling-type power sensor for low power. The research of impedance compensation also reduces the effect of the introduced extra capacitance on the cascaded power sensor.(4) In terms of frequency detectors based on MEMS microwave power sensing technologyA one-two type microwave frequency detector is designed, fabricated, packaged and tested. The measured return loss is about-17dB at the center frequency. For the signal with low power, the measured sensitivity is about 0.033μMHz-1"10dBm,0.110μV·MHz-1@15dBm and 0.343μV·MHz-1@20dBm while the sensitivity is 0.013fF·MHz-1@24dBm for the signal with high power. On this basis, a one-three type microwave frequency is proposed. The frequency detector is fabricated and tested. The measured return loss is less than -28dB at the center frequency of 12GHz. When the frequency varies from 11 GHz to 13GHz, for the signal with low power (20dBm), the measured voltage ratio of the thermoelectric MEMS microwave power sensor decreases from 1.25 to 0.7 and the measured sensitivity is close to 0.323/GHz. For the signal with high power (26dBm), the capacitance ratio of the capacitive MEMS microwave power sensor decreases from 1.15@11GHz to 0.8@13GHz and the measured sensitivity is close to 0.2/GHz. Meanwhile, an in-line type frquency detector is proposed and the experiment shows that the return loss is less than-14dB and the insertion loss is about 1.2dB over X-band. For the incident power of lOdBm, the output voltage increases from 0.21mV to 0.35mV when the frequency increases from 8GHz to 12GHz. The measured sensitivity is close to 0.035mV/GHz. The innovations is that the proposed one-three type microwave frequency not only improve the test accuracy but also realize the frequency detection for the unknown-power signal. The proposed in-line type frquency detector has little impact on the signal being transmitted. The proposed detectors are consisted of passive devices and consumes no DC power.(5) In terms of S-parameters of frequency detectors based on MEMS microwave power sensing technologyThe characteristic impedance and attenuation coefficient of the CPW, ACPS and Edge Coupled CPW transmission line is extracted. On this basis, the S-parameters of the power divider is deduced by adopting odd-even model method. According to microwave network theory, the S-parameters of the one-two type and one-three type microwave frequency detector are calculated. The influnce of the phase shift, the impedance and length of the ACPS transmission line in the power divider on the microwave performance of the frequency detectors is investigated. The innovations is that the S-parameters of the MEMS frequency detectors are analyzed and researched. The voltage standing wave is suppressed by reducing the return loss, which slove the design problems in microwave signal detecting and analyzing systems. This work lays the theoretical foundation for realization of electromagnetic compatibility in the systems.The devices presented in this dissertation are analyzed, calculated, simulated, fabricated and tested. The above design theory and implementation method of microwave frequency detectors based on MEMS microwave power sensing technology contain high science value and have been reported in the international Journals in MEMS field such as IEEE Sensors Journal、Journal of Micromechanics and Microengineering and international conference such as IEEE Sensors and IEEE RFIC. Meanwhile, based on these results, a number of national invention patents of the People’s Republic of China have been authorized. These research achievements with the independent intellectual property rights fill the blank of China’s microwave frequency detection based on MEMS technology, and have a number of potential applications.