496
P. Joshi et al.
manufacturing process. Sensing and actuation properties of ZnO thin film strongly
depend on the crystalline structure of ZnO film. Menon et al. (2011) deposited ZnO
films on silicon and glass substrate and discussed origin of stress. The crystalline
structure depends on growth parameters such as sputter pressure, ambient temperature, gas flow rate, and target substrate distance, etc. (Menon et al. 2008; Singh et al.
2007). Over the past decades, ZnO thin film and its different properties have been
researched extensively. Singh et al. (2015) directly measured the stress of ZnO film
by curvature method and correlated with the ZnO optical properties. Ondo-Ndong
et al. (2003) prepared the ZnO films using metallic zinc target and effect of process
parameters on film properties was analyzed. Rao et al. (2009) investigated the effect
of stress on optical band gap of ZnO and the thin films were prepared by spray pyrolysis method. Ashrafi et al. (2004) deposited epitaxial ZnO layers on 6H-SiC substrates
and analyzed strain relaxation effect on exciton resonance. Epilayers of GaN on Si
(111), 6H-SiC (0001) and c-plane sapphire were grown by Zhao et al. (2003) and
stress effect on optical properties was studied. Maniv et al. (1982) reported that the
sputtering pressure and incidence angle affect the reactive ZnO layers. Nucleation
and growth of AlN thin films were investigated and influence of process parameters
was explored (Engelmark et al. 2000; Iborra et al. 2004). Loebl (2003) investigated
AlN c-axis orientation effect on Electromechanical coupling coefficient. With optimal sputter deposition parameters stress-free ZnO thin film was obtained (Drese and
Wuttig 2005; Krupanidhi and Sayer 1984). Jou et al. (1992) used sputter pressure
17 mTorr and Ar oxygen ratio 1:1 for stress-free ZnO thin films. Though, residual
stress also affects the optical properties of ZnO thin films (Ghosh et al. 2004; Shan
et al. 1996). The Band gap of ZnO film shows red/blue shift with increasing compressive/tensile biaxial stress. Li et al. (2007) estimated tensile stress in ZnO films
deposited on quartz by X-ray diffraction technique and a blue shift was observed in
optical band gap with increasing tensile stress. Mohanty et al. (2009) investigated
the thickness-dependent stress in ZnO films on Si/SiO 2 and found compressive stress
~−2.0 × 10
10 dynes/cm
2 in ~1 μm thick films. It is very useful to investigate the
change in lattice constants with residual stress. Ping et al. (2012) reported that lattice
constant(c) has linear relation with compressive stress. Rieger et al. (1996) explored
the influence of biaxial compressive stress on optical band gap and lattice constant
of GaN thin film. With increasing biaxial compressive stress, band gap (blue shift)
as well as lattice constant increases.
Further, stress relaxed ZnO thin film shows enhanced performance and resulting
devices are highly reliable and reproducible (Ashrafi et al. 2004; Maniv et al. 1982;
Trodahl et al. 2006). Device yield and long term reliability can be improved by stress
engineering. In-plane stress primarily produced in ZnO thin films caused by the
conditions imposed by underlying substrate and ambient conditions. Large in-plane
stress develops in ZnO thin films due to intrinsic or extrinsic effects (Ondo-Ndong
et al. 2003; Rao et al. 2009). Usually, MEMS devices consist of metal, dielectric,
and functional multilayers. Consequently, to avoid multilayer’s inter-diffusion, ZnO
processing temperature must be low (Mass et al. 2003). Sharp, clean, and crack-free
interfaces are highly desirable for long term reliability of MEMS devices. Further,
when MEMS devices are exposed to high ambient temperature, there is a possibility
P. Joshi et al.
manufacturing process. Sensing and actuation properties of ZnO thin film strongly
depend on the crystalline structure of ZnO film. Menon et al. (2011) deposited ZnO
films on silicon and glass substrate and discussed origin of stress. The crystalline
structure depends on growth parameters such as sputter pressure, ambient temperature, gas flow rate, and target substrate distance, etc. (Menon et al. 2008; Singh et al.
2007). Over the past decades, ZnO thin film and its different properties have been
researched extensively. Singh et al. (2015) directly measured the stress of ZnO film
by curvature method and correlated with the ZnO optical properties. Ondo-Ndong
et al. (2003) prepared the ZnO films using metallic zinc target and effect of process
parameters on film properties was analyzed. Rao et al. (2009) investigated the effect
of stress on optical band gap of ZnO and the thin films were prepared by spray pyrolysis method. Ashrafi et al. (2004) deposited epitaxial ZnO layers on 6H-SiC substrates
and analyzed strain relaxation effect on exciton resonance. Epilayers of GaN on Si
(111), 6H-SiC (0001) and c-plane sapphire were grown by Zhao et al. (2003) and
stress effect on optical properties was studied. Maniv et al. (1982) reported that the
sputtering pressure and incidence angle affect the reactive ZnO layers. Nucleation
and growth of AlN thin films were investigated and influence of process parameters
was explored (Engelmark et al. 2000; Iborra et al. 2004). Loebl (2003) investigated
AlN c-axis orientation effect on Electromechanical coupling coefficient. With optimal sputter deposition parameters stress-free ZnO thin film was obtained (Drese and
Wuttig 2005; Krupanidhi and Sayer 1984). Jou et al. (1992) used sputter pressure
17 mTorr and Ar oxygen ratio 1:1 for stress-free ZnO thin films. Though, residual
stress also affects the optical properties of ZnO thin films (Ghosh et al. 2004; Shan
et al. 1996). The Band gap of ZnO film shows red/blue shift with increasing compressive/tensile biaxial stress. Li et al. (2007) estimated tensile stress in ZnO films
deposited on quartz by X-ray diffraction technique and a blue shift was observed in
optical band gap with increasing tensile stress. Mohanty et al. (2009) investigated
the thickness-dependent stress in ZnO films on Si/SiO 2 and found compressive stress
~−2.0 × 10
10 dynes/cm
2 in ~1 μm thick films. It is very useful to investigate the
change in lattice constants with residual stress. Ping et al. (2012) reported that lattice
constant(c) has linear relation with compressive stress. Rieger et al. (1996) explored
the influence of biaxial compressive stress on optical band gap and lattice constant
of GaN thin film. With increasing biaxial compressive stress, band gap (blue shift)
as well as lattice constant increases.
Further, stress relaxed ZnO thin film shows enhanced performance and resulting
devices are highly reliable and reproducible (Ashrafi et al. 2004; Maniv et al. 1982;
Trodahl et al. 2006). Device yield and long term reliability can be improved by stress
engineering. In-plane stress primarily produced in ZnO thin films caused by the
conditions imposed by underlying substrate and ambient conditions. Large in-plane
stress develops in ZnO thin films due to intrinsic or extrinsic effects (Ondo-Ndong
et al. 2003; Rao et al. 2009). Usually, MEMS devices consist of metal, dielectric,
and functional multilayers. Consequently, to avoid multilayer’s inter-diffusion, ZnO
processing temperature must be low (Mass et al. 2003). Sharp, clean, and crack-free
interfaces are highly desirable for long term reliability of MEMS devices. Further,
when MEMS devices are exposed to high ambient temperature, there is a possibility