This work demonstrates the processing,modeling,and characterization of nanocrystalline refractory metal tantalum(Ta)as a new structural material for microelectromechanical system(MEMS)thermal actuators(TAs).Nanocrysta...This work demonstrates the processing,modeling,and characterization of nanocrystalline refractory metal tantalum(Ta)as a new structural material for microelectromechanical system(MEMS)thermal actuators(TAs).Nanocrystalline Ta films have a coefficient of thermal expansion(CTE)and Young’s modulus comparable to bulk Ta but an approximately ten times greater yield strength.The mechanical properties and grain size remain stable after annealing at temperatures as high as 1000°C.Ta has a high melting temperature(Tm=3017℃)and a low resistivity(ρ=20µΩcm).Compared to TAs made from the dominant MEMS material,polycrystalline silicon(polysilicon,Tm=1414℃,ρ=2000µΩcm),Ta TAs theoretically require less than half the power input for the same force and displacement,and their temperature change is half that of polysilicon.Ta TAs operate at a voltage 16 times lower than that of other TAs,making them compatible with complementary metal oxide semiconductors(CMOS).We selectα-phase Ta and etch 2.5-μm-thick sputterdeposited films with a 1μm width while maintaining a vertical sidewall profile to ensure in-plane movement of TA legs.This is 25 times thicker than the thickest reactive-ion-etchedα-Ta reported in the technical literature.Residual stress sensitivities to sputter parameters and to hydrogen incorporation are investigated and controlled.Subsequently,a V-shaped TA is fabricated and tested in air.Both conventional actuation by Joule heating and passive self-actuation are as predicted by models.展开更多
基金supported by the US National Science Foundation(NSF)grant number CMMI-1635332the Kavcic-Moura Endowment Fund for the support.
文摘This work demonstrates the processing,modeling,and characterization of nanocrystalline refractory metal tantalum(Ta)as a new structural material for microelectromechanical system(MEMS)thermal actuators(TAs).Nanocrystalline Ta films have a coefficient of thermal expansion(CTE)and Young’s modulus comparable to bulk Ta but an approximately ten times greater yield strength.The mechanical properties and grain size remain stable after annealing at temperatures as high as 1000°C.Ta has a high melting temperature(Tm=3017℃)and a low resistivity(ρ=20µΩcm).Compared to TAs made from the dominant MEMS material,polycrystalline silicon(polysilicon,Tm=1414℃,ρ=2000µΩcm),Ta TAs theoretically require less than half the power input for the same force and displacement,and their temperature change is half that of polysilicon.Ta TAs operate at a voltage 16 times lower than that of other TAs,making them compatible with complementary metal oxide semiconductors(CMOS).We selectα-phase Ta and etch 2.5-μm-thick sputterdeposited films with a 1μm width while maintaining a vertical sidewall profile to ensure in-plane movement of TA legs.This is 25 times thicker than the thickest reactive-ion-etchedα-Ta reported in the technical literature.Residual stress sensitivities to sputter parameters and to hydrogen incorporation are investigated and controlled.Subsequently,a V-shaped TA is fabricated and tested in air.Both conventional actuation by Joule heating and passive self-actuation are as predicted by models.
