The adjustable range on post-fabrication resonance wavelength trimming of long-period fiber gratings was broadened toward the blue side, and the mechanisms of the resonance wavelength shifts caused by heating were investigated. It can be concluded that the glass structure relaxes more slowly than the residual stress with decreasing heating temperature and the blue shift caused by the residual stress relaxation appears more strongly at the early stage of heating. The blue shift of 41 nm was obtained by heating a long-period grating at 600 for 3500 minutes. The changes of the index difference inducing the wavelength shifts of -41 nm and 35 nm were estimated at about -1.210-4 and +1.0 10-4 by numerical analysis, respectively.

Long-period gratings (LPGs) are written in the fibers un-preheated and preheated. The influence of residual stress on trimming resonance wavelengths by heating the LPGs is investigated comparing the post-heating changes of the transmission characteristics. It becomes evident that the residual stress relaxation shifts resonance wavelengths to shorter wavelengths quickly and the glass structure modification moves them to longer wavelengths slowly. The relaxation rate of the glass structure drops rapidly with the decrease in heating temperature, and the influence of the residual stress relaxation appears more strongly at the early stage of heating at a lower temperature. The trimming wavelength range can be broadened on the short wavelength side by decreasing the heating temperature. We could adjust resonance wavelengths without significant peak loss changes by the residual stress relaxation before writing LPGs, though the trimming range becomes narrow.

This paper presents the design, fabrication and characterization of a low actuation voltage capacitive shunt RF-MEMS switch for microwave and millimeter-wave applications based on a corrugated electrostatic actuated bridge suspended over a concave structure of coplanar waveguide (CPW), with sputtered nickel as the structural material for the bridge and gold for CPW line, fabricated on high-resistivity silicon (HRS) substrate using IC compatible processes for modular integration in a communication devices. The residual stress is very low because having both ends corrugated structure of the bridge in concave structure. The residual stress is calculated about 3-15 MPa in corrugated bridge and 30 MPa in flat bridge. The corrugated bridge of the concave structure requires lower actuation voltages 20-80 V than 50-100 V of the flat bridge of the planar structure in 0.3 to 1.0 µm thick Ni capacitive shunt RF-MEMS switch, in insertion loss 1.0 dB, return loss 12 dB, power loss 10 dB and isolation 28 dB from 0.5 up to 40 GHz. The residual stress of the bridge material and structure is critical to lower the actuation voltage.

We have improved the mechanical reliability of deep-submicron semiconductor devices by applying a simulation technique. Typical kinds of damages that reduce the reliability are dislocations in silicon substrates, delamination or cracking of thin films, and deterioration of electronic characteristics of devices. The mechanical stress that develops in device structures is caused by not only mismatches in thermal expansion coefficients among thin film materials but also intrinsic stress of thin films such as poly-silicon and silicides. Fine patterning by dry etching makes sharp edges and they also cause stress concentration and thus high stress. The manufacturing processes in which stress mainly develops are isolation, gate formation, and interconnect formation. We have developed methods for reducing the stress in each of the above-mentioned process. This stress reduction is very effective for highly reliable manufacturing. Finally, we clarify the effect of the residual stress in transistor structures on shift in the electronic characteristics of MOS transistors.

It is necessery to investigate the buckling mechanism in order to obtaining good performance from various sensors composed of resistors and microbridges or membranes. Especially for flow sensors, a convex formed bridge has an advantage over a flat or concave bridge with respect to heat transfer coefficient. We have fabricated various shapes of bridges and have prepared SiNx sputtered films as the support films of microbridges and Pt sputtered or evaporated films as resistors. We have achieved deformation control for both the longitudinal axis and transverse axis of Pt/SiNx double layered microbridges by appropriate selection of the total residual stress of Pt/SiNx structures and of the stress gradient between the Pt film and SiNx film. The deformation direction of the longitudinal axis of bridges for the beam bridge (Type ) are all the same as that of cantilevers and may be predicted via the stress gradient between the Pt and SiNx filmes of the bridges. The deflection of the transverse axis of the table bridge supported by four beams (Type ) changes linearly with the total stress of the Pt/SiNx structure and the deformation changes for the transverse axis are the same as that of completely free films as predicted from the stress gradient between the Pt film and the SiNx film. The interesting result is that the deformation direction for the longitudinal axis of Type is opposite to that of Type with the same film structure. We discuss the reason for this opposition via differences in the progress of the anisotropic etching. We consider that this result will expand the range of manufacturable shapes and film structures of microbridges.