Research On The Self-Powered Low-Power Thermoelectric-Photoelectric Micro Sensor For RF T/R Modules In The Internet Of Things

As a vital component of wireless transceiver systems,RF transmitter/receiver?T/R?modules are widely used in communications and radar systems.The power consumption of the modules is mainly determined by the power amplifier?PA?.Because the conversion efficiency of PA is limited,a considerable part of working power is dissipated in the form of heat,which not only causes the component to heat up and affects the normal operation,but also causes the waste of energy.In addition,monitoring the transmit power of PA and harmonic distortion is of great significance,which can avoid burning out of device due to excessive power and detect the device's aging and failure.In order to solve the problems above,a self-powered low-power thermoelectric-photoelectric micro sensor for RF T/R modules in the Internet of Things?IoT?is proposed,in which MEMS thermoelectric microwave sensors and thermoelectric-photoelectric integrated micro energy harvester based on thermocouples are the core components of the sensor system.They are used for microwave power and frequency measurement,and energy harvesting,respectively.The main works are described as follows:1.Research on the S-parameter model of MEMS indirect-heating microwave power sensor:An equivalent circuit model is proposed to obtain the S-parameters of the MEMS indirect-heating microwave power sensor.The insert loss of the transmission line,the parasitic parameters of the terminal resistors,and the electromagnetic coupling effect between the terminal resistors and the thermopile are considered.The model results show that S₁₁1 is affected by the distance between terminal resistors and thermopile,but does not change obviously with the length of thermopile and incident power.In order to verify the circuit model,the S-parameters of sensors with different structure parameters are measured from 1 GHz to 30 GHz.The results show that the measured S-parameters are in good agreements with the results by model.The average error is less than 5%in the range of 1-20 GHz.For the power sensor with 100?m in length of thermopile and10?m in the distance between terminal resistance and thermopile,the S₁₁1 by model and measurement are-31.1 dB and-30.6 dB,respectively.Furthermore,the resistance error of terminal resistor caused by fabrication processes has a great influence on S₁₁.The equivalent model can be used to optimize the performance of the indirect-heating thermoelectric power sensor and enhance electromagnetic compatibility for system integration.2.Research on the response time of MEMS indirect-heating microwave power sensor:The response time of MEMS indirect-heating microwave power sensor is comprehensively researched from the perspective of time domain and frequency domain.In the time domain,an equivalent 1D model is established to simplify the transient heat transfer problem and is accurate enough for understanding the thermal time constant and studying the influence of some key structure parameters on the response time.In the frequency domain,the transient heat transfer equation is established by analyzing the heat transfer process of the power sensor with a simple lumped-heat-capacity model,and an equivalent circuit model is further built by electro-thermal analogy method.Then the analytical expressions for the frequency response of the indirect-heating thermoelectric power sensor are derived from the circuit model,and corresponding time constant or response time can be acquired from the 3 dB cut-off frequency.Although it is difficult to obtain the parameters in analytical expressions accurately in theory,the lumped-heat-capacity model and equivalent lumped circuit model can provide better insight into the behavior of frequency response and guide the measurement of response time.Finally,the response time of power sensors with different structures is measured by three methods:transient response with RF step signal,transient response with DC step signal,and frequency response.The results indicate that the response time increases with the length of thermopile and distance between terminal resistors and thermopile.The frequency response can determine the response more stable than the transient response in time domain.The rise time by the transient response with RF step signal has relatively large fluctuation.The reason is due to the irregular jitter in the rise edge of output waveform caused by the non-ideal production with RF step signal.The changing trend of response time is consistent well with the equivalent 1D model.For the power sensor with 100?m in length of thermopile and 10?m in the distance between terminal resistance and thermopile,the response time by the equivalent 1D model,the rise time and fall time by the transient response with RF step signal,the rise time and fall time by the transient response with DC step signal,the 3 dB cut-off frequency and corresponding response time by frequency response are 353?s,1.04 ms,255?s,261?s,236?s,1550 Hz,236?s,respectively.In addition,the measured burn-out power is about 1.1 W.3.Research on improving the dynamic range of MEMS indirect-heating microwave power sensor:A microwave power sensor based on MEMS thermopile and curled cantilever beam is proposed for the first time.The power sensor consists of a thermoelectric power sensor and a capacitive power sensor for low and high power detection,respectively.To improve the dynamic range and optimize the impedance matching characteristic,the curled cantilever beam is utilized and the slot width of the coplanar waveguide transmission line is modified.Furthermore,analytical models for the self-assembling microwave power sensor with consideration of curled cantilever are proposed,including the electromagnetic model for predicting the impedance matching characteristic and static mechanical model for the output characteristic of the capacitive power sensor.The experimental results show a good agreement with the theory and validate the effectiveness of the presented models.Furthermore,good performance of the power sensor has found.The measured return loss is lower than-25.5 dB at 8–12 GHz and the output of the power sensor has good linearity with the incident radio frequency power up to 600 mW.The sensitivity by model is about12.9 fF/W and the error between theory and linear fit is about 3.1%.4.Research on the microwave frequency sensor based on MEMS thermopile and MIM capacitor:An inline frequency sensor composed by MEMS thermopile and MIM capacitor is proposed.The operation principle of the frequency sensor is based on sensing the power coupled by the MIM capacitor.The novel frequency sensor can achieve absolute frequency measurement with a simple structure and no DC power consumption.The sensor design is guided by ANSYS Workbench co-simulation and a lumped circuit model.Fabrication of the frequency sensor is completely compatible with the GaAs monolithic microwave integrated circuit process.The results validate the effectiveness of the simulation and model and show a relatively good performance of the frequency sensor with simple and reliable components.The measured S₁₁1 and S₂₁1 measured at 1-12 GHz are better than-15 dB and-1.33 dB,respectively.In addition,an equivalent hybrid circuit model with phase analysis for inline frequency sensor in order to comprehensively evaluate reflection and insertion losses and phase characteristics of the sensor.The equivalent hybrid circuit model,which consists of distributed parameter elements and lumped parameter elements,takes the attenuation mechanisms of the transmission lines into consideration.The effectiveness of the equivalent model has been validated by the results of simulation and experiment.The phase shift of the device changes linearly from 2.9°to 33.4°when frequency increases from 1 GHz to 12 GHz.This method can be used to guide modeling of similar microwave devices.5.Research on the design theory and implementation method of the thermoelectric-photoelectric integrated micro energy harvester:Firstly,the micro thermoelectric generator is systematically reviewed to provide the reference for the design,fabrication,and measurement of thermoelectric-photoelectric integrated micro energy harvester.In terms of design theory,a novel structure of thermoelectric-photoelectric integrated micro energy harvester and two adjusted structures are proposed,which are mainly composed of a solar cell and a hybrid structure micro thermoelectric generator.The two parts are fabricated on a single chip to realize the monolithic integration of thermoelectric-photoelectric functions.Then an equivalent circuit model under multi-field coupling conditions is established to analyze the output characteristics of the micro thermoelectric generator and the solar cell,which can realize multi-parameter collaborative design and optimization.The thermoelectric coupling simulation under the ANSYS Workbench co-simulation platform and Silvaco TCAD photoelectric simulation are used to simulate the output characteristics of the micro thermoelectric generator and the solar cell,respectively.The results of simulations further verify the design of proposed structure.Because the material properties directly affect the performance of the device and determine the optimal structure,as indicated by the equivalent circuit model and simulation,a series of test structures are designed to characterize the resistivity,specific contact resistivity and Seebeck coefficient of polysilicon to guide the further optimization of device structure,materials,and fabrication processes.In term of implementation method,the thermoelectric-photoelectric integrated micro energy harvester and test structure of material properties are all fabricated by the conventional MEMS technology.In order to determine the temperature difference between the two ends of the devices under test,a feasible measurement platform is designed to characterize the performance of its thermoelectric output.The maximum output power factor and voltage factor of the standard structure are 6.3×10^-3?Wcm^-2K^-22 and 0.316 Vcm^-2K^-1,respectively.The IV characteristic of the solar cell under two different light-receiving surface are measured respectively.Finally,the application of the thermoelectric-photoelectric integrated micro energy harvester in RF transceiver is demonstrated.Furthermore,two methods to improve the output performance of the devices are discussed.The first is to replace the high-doped polysilicon interdigital electrode of solar cell with metal?The conversion efficiencies of standard structure under two different light-receiving surface have improved from 4.11%and 0.5%to 5.9%and 1.01%,respectively?,and the second is to cover the polyimide thermal insulation layer with Al heat transfer plate(The maximum output power factor and voltage factor of the standard structure have improved to7.48×10^-3?Wcm^-2K^-22 and 0.35 Vcm^-2K^-1,respectively).It perfects the design theory and implementation method for the self-powered low-power thermoelectric-photoelectric sensor scheme.