Research On Perovskite ALT Heat Flow Sensitive Thin Films And Devices

Atomic layer thermopile（ALT）heat flux sensors are used in the heat flux measurement of aero-engine hot section and the measurement of high-frequency pulsating heat flux in hypersonic wind tunnel tests due to their high sensitivity,simple structure and fast response.In the above application scenarios,the smaller the sensor is,the lower interference to the flow field.It is of great significance to develop a high-performance ALT heat flux sensors with miniaturization,high sensitivity and fast response.At the same time,realization of mass production could reduce the cost greatly.This paper mainly studies the following work:1.High-performance Sr_xLa_1-xTiO₃（LSTO）thin film preparation was investigated using a MOCVD system.By adjusting the La doping ratio,heating temperature and other process conditions,with optimal parameters of the heating current being 28A and the La doping ratio being 60%,the surface morphology is relatively flat and the holes gradually disappear.X-ray diffraction（XRD）scan shew that films were grown along with the c-axis,and the out-of-plane full width at half maximum（FWHM）Δωand in-plane FWHMΔφwere 0.63 and 0.83,respectively.Subsequently,heat flux measurement was performed on LSTO thin films grown on Sr TiO₃（STO）and La AlO₃（LAO）single crystal substrates with 12°tilting angle.Under the effective sensor size of 4mm×2mm,given a heat flux of 38.1 k W/m~2,the maximum sensitivity coefficients were 115.49μV/（k W/m~2）and 26.25μV/（k W/m~2）,respectively.Compared with that of the same size YBa₂Cu₃O_7-δ（YBCO）thin film,11.02μV/（k W/m~2）,the sensitivity coefficient is much higher,which is of great significance for further research on miniaturized and high sensitivity coefficient ALT heat flux sensors.At the same time,the measurement of the LSTO film at high temperature was completed.It was found that the upper limit of the working temperature of the LSTO film should be in 550～600°C.And the error of its sensitivity coefficient at high temperature and room temperature was within 6%,which proved its stability.2.To further improving the sensitivity coefficient and miniaturizing the device size,the structure of the patterned device with multi-line physical mode was studied.The designed device structure has the characteristics of large-scale batch fabrication on a 2inch wafer,so that thousands of miniaturized ALT devices with the size of 1mm×1mm can be produced at one time.Then,the microfabrication process of the device preparation was explored,and the optimal lithography,etching,stripping process and slicing parameters were obtained to ensure the yield of the device preparation.3.The performance of miniaturized ALT devices has been tested and analyzed.Two-device linear array samples and single-device samples were tested by UV laser.The potential output of the two-device samples was doubled compared to single-device samples.The sensitivity was positively correlated with the line length,and the response times were in the order of hundreds of nanoseconds.Compared with the 4mm YBCO film with a single line,the sensitivity coefficient is improved,and the sensitivity coefficient of the device of 1mm×1mm is calibrated and measured to reach 11μV/（k W/m~2）.Finally,the lithography process was transplanted to the LSTO film for preliminary exploration.