Research On Fabrication Technology Of Resonant Thin Film Thermal Converters

Thermal converter is a reference standard for measuring AC voltage or current and the core device of AC-DC transferstandard around the world.Using high-resolution and high-precision temperature measurement technology to reduce the AC-DC transfer difference,improving the measurement accuracy,simplifing the device manufacturing process and reducing production costs are always the research hotpots of thin-film thermal converter.In this dissertation,a resonant thin-film thermoelectric converter is proposed,which is based on the principle of electro-thermal excitation/piezoresistive detection of micro-bridge resonator.The heat of the heating resistance increases the average temperature of the micro-bridge,thus the axial compressive stress increases(or axial tensile stress decreases),and the resonant frequency decreases,the temperature informationof the heating resistancecan be acquired by measuring the micro-bridge resonantfrequency changes.Firstly,the fabrication process of thin film heating resistors with low resistance temperature coefficient was studied.NiCrSi films with different thicknesses were prepared by DC and RF magnetron sputtering.The films were annealed at 450°C in nitrogen atmosphere fordifferent temperatures.The resistances of the films at different temperatures were measured before and after annealing and the resistance coefficients of the films were calculated.We found that the TCR of Ni Cr Si films with the thickness of 89.1nm,deposited by RF magnetron sputtering and annealed for 30 minutes is only-0.86 ppm/?C,which ishelpfulto achieve the low AC-DC transfer difference.The dissertation focuses on the fabrication technology of resonant thin-film thermal converter.The preparation process and stress compensation technology of adiabatic film as well as the production processof polysilicon resistance were studied.In order to protect the Al lines and polysilicon resistanceson the front of the devices during corrosion process using KOH solution,a combination of wet etching and dry etching is used.First,the device was etched 35μm deep from the back side using a mechanical fixture and AR-PC504 corrosion-resistant adhesive,and then the release of the micro bridge resonator and the fabrication of the device were carried out using back dry etching technology.The whole processing verified the feasibility of the fabrication technology of the resonant thin-film thermoelectric converter,which lays the foundation for the subsequent packaging and testing.