High Sensitive Force-electric Coupling Effect Of GaAs-RTD Epitaxy On Si Substrate

Geared to the application and development needs of MEMS sensor for high sensitivityand low consumption in the areas of national defense military, aerospace, deep spaceexploration and so on. The high sensitivity characteristics of RTD based on GaAs havestudied by our team on the basis of key project of national science foundation《The basisresearch of highly sensitive sensors of the micro-nano mechanical structures embeded withthe e-index semiconductor devices》（50730009）. The RTD （resonant tunneling diode）structure of which the high-pressure resistance property was tested and verified was used asthe sensitive element to manufacture the high sensitivity devices. In research, series ofproblems about GaAs as MEMS material which we confront: brittlement, immature technique,high-cost, etc. To solve the problems, an new technique is GaAs epitaxy on Si substrate whichintegrates the merits of Si material, such as the capacity of over-load, low-cost and maturetechnique, with highly sensitive devices of GaAs, based on the national science fund project《The basis effects of the tunneling gyscope with the QD-RTD of Ⅲ-Ⅴ group materialsbaesd on Si substrate》（61171056）. Thus, the technique of GaAs epitaxy on Si substrate and itsforce sensitive effect of structure has been studied.In the paper, the superlattice structure is adopted to optimize the GaAs epitaxy on Sisubstrate. The result shows that the defect density and the residual stress both reduce and thequality is greatly improved. In the experiment, the dislocation line in the Si/GaAs material hasbeen bent by the superlattice structure and not extended to the surface using the TEM andSEM technology. Also, the defect density reduces from106cm-2to104cm-2and the residualstress decreased from1.57GPa to232Mpa. That mean that the superlattice structure is anefficient method to optimize the material. At the same time, the mechanical property wassimulated as well as the Si, and the test of force sensitive proved the better piezoresistive coefficient. They all predict the greater electromechanical coupling effect of the material ofSi/GaAs.In the experiment, the quantum well tunneling structure—RTD grows on optimizedsubstrate and the piezoresistive coefficient of RTD based on Si substrate are great whicn canbe compared with previous GaAs-RTD. In the paper, the principle of electromechanicalcoupling of Si-RTD is established and the structure of RTD is prepared. The characteristics ofcross section, surface and residual stress are analyzed by the AFM and Raman technology. Atthe same time, the electromechanical coupling effect of Si-RTD is tested and thepiezoresistive coefficient is calculated to6.85×10^-9m²/N which is compare with that ofGaAs-RTD (2.54×10^-9m²/N).The scale of quantum dot structures in the three-dimensional direction is less than thefree path of electrons and the quantum effect is more obvious. The electrical properties ofRTD with the quantum dots （QD） is superior than traditional quantum well RTD, of which theelectron mobility is higher. So the higher sensitivity is expected to achieve and theelectromechanical coupling effect of QD-RTD structure is preliminarily verified. In the paper,the electron tunneling principle of QD-RTD is established first, and the structure of QD-RTDis prepared with the growth technology and principle of quantum dot. The quantum dot hasbeen embed in the RTD which is analyzed using AFM and spectral characterization technique.Also, the force sensitive property of QD-RTD structure is veritied.With the development of MEMS sensors, the novel detection technology has beenpresented in the paper. The high sensitivity characteristics of Si-RTD has been verified in theexperiment. Also, the processing technology is better and the cost is less. It is a sample todevelop a new generation of MEMS sensors with low cost and high sensitivity.