Gas Microsensor Based On Femtosecond Laser Induced Nanoparticle Deposition

In recent years,with the rapid development of microelectronics and micromachining technology,the research of gas microsensors has attracted great attention.Due to the advantages of miniaturization,low power consumption and integration,gas microsensors have obvious advantages in real-time monitoring and detection,especially the development of electronic nose,wearable devices,swallowable electronic capsules and other microdevices need to be compatible and integrated in gas microsensors with good sensing performance.With the development of micro fabrication technology,more and more gas microsensors have been developed.Although chemical vapor deposition,electrospinning and patterned nanowire electrodeposition methods and so on,can be used to prepare gas microsensors with good sensing performance,the disadvantages of their preparation methods also restrict the development of microsensors.At present,the problems faced by microsensors include:(1)the limitations of material selection,microstructures need to be prepared by certain methods according to the growth mechanism of materials or forming conditions,which are usually suitable for a specific materials,and lack of universal applicability of materials;(2)the lack of flexibility to fabricate microstructures,random deposition of microstructures or large-area etching processes will lead to poor design and positioning of microdevices,making it difficult to apply to multifunctional integration;(3)Poor process compatibility.Beacause of some micro-preparation method depend on specific preparation conditions and microstructure characteristics,it is difficult to meet the compatibility with traditional CMOS processes to form a multi-functional integrated sensor chip;(4)chemical reagent pollution,because of the traditional method in the preparation and design of microstructure is often accompanied by chemical additives,catalyst and mask,the microsensor is easy to be polluted by chemicalsIn order to solve the above problems,this paper proposes a laser-induced deposition technology,which has such advantages:wide selection of materials,high flexibility,CMOS process compatibility,mask-free,no chemical additives,and programmable control,to fabricate gas microsensor.Using ammonia,hydrogen and ethanol in human gastrointestinal tract as target detection gases,three kinds of nanoparticles(Pd-WO3·xH2O),Pd and zinc oxide(ZnO)as gas sensitive materials,the gas microsensors with good performance has been prepared by laser-induced deposition.The main achievements are as follows:1.Pd-WO3·xH2O microwires sensor was prepared,which can realize fast and low limit of detection of NH3 detection.It provides a feasible strategy for the fabrication of microsensors.The Pd-WO3·xH2O microwires sensor has good selectivity for NH3 at 25?.The ultra-fast response/recovery time(1.4 s/3.3 s)and 1 ppm low limit of detection can be achieved by adjusting the length of the microwire.The larger the length of the microwire,the greater the response value of the sensor to the target gas2.Fabrication of Pd microwires hydrogen sensor with low limit of detection and wide detection range.Pd nanoparticles with good dispersion were prepared by ultrasonic assisted one-step solution synthesis method,and the microwires was prepared by laser-induced deposition of Pd nanoparticles,which has hydrogen sensing properties.There are two sensing mechanisms for hydrogen sensing in the microwire sensor,which are the formation of PdHx and the control of the conductivity of microwires by lattice expansion.Hydrogen sensing with low limit of detection of 1.4 ppm and wide detection range of 0.001%-4.0%at room temperature is realized.3.The ZnO nanowire array gas sensor was fabricated to realize the ethanol sensing with fast,high response and low limit of detection.ZnO nanoparticles were deposited on the substrate by laser-induced deposition.Furthermore,ZnO nanowires were grown in solution with the deposited ZnO nanoparticles as seeds to obtain the microstructure based on nanowire arrays.The morphology of the nanowires was optimized by adjusting the laser processing power and the growth time in solution.Deposited ZnO with rough surface,porous and stacked morphology were formed by processing ZnO nanoparticles at appropriate power(about 14-17 mW).The ZnO nanowires with good morphology could be formed only after the deposited ZnO were grown in solution for 2.5 h.The results show that the fabricated ZnO nano wire array has ability of gas sensing,and can achieve rapid response/recovery time of 14.4 s/14.5 s in 80 ppm ethanol at 300?,with high response of 12%and low limit of detection of 10 ppm.