Daniel Rosén

Dependence of the electromechanical coupling on the degree of orientation of c-textured thin AlN films

Highly c-oriented thin aluminum nitride (AlN) films have been grown at room temperature with reactive sputter deposition. Membrane film bulk (FBAR) thickness excited resonators have been subsequently fabricated by bulk micro machining of silicon (Si). The resonators were then electrically characterized with a network analyzer in a one-port configuration. Subsequently, the coupling coefficients and the Q factors of both the longitudinal and the shear mode were extracted from fitting the measured admittance with that of the equivalent circuit model at the resonance frequencies. The goal of this work is to study the variation of the electromechanical coupling and the quality factor of the resonators, for both the longitudinal and the shear modes as a function of the degree of film texture. It is observed that the films exhibit a mean tilt of the c-axis relative the surface normal. This tilt is found to depend on both the film texture and the distance from the wafer radius. It is also demonstrated that the textured films exhibit a behavior of the electromechanical coupling effectively identical to that of a single crystalline material of equivalent tilt. Thus, it is shown that the electromechanical coupling for the longitudinal mode decreases from 8% to 4%, and that for the shear mode increases from 0% up to 3% by varying the full width half maximum (FWHM) of the [002] rocking curve in the interval from 2/spl deg/ to 10/spl deg/.

Membrane covered electrically isolated through-wafer via holes

An electrically isolated through-wafer via hole, covered by a membrane, has been realized by standard integrated circuits processes together with deep silicon etching. The deep silicon etching was performed by the Bosch silicon etch process in a Plasma-Therm etch system. The via structures were made in double-sided polished 300 µm thick silicon wafers and had widths down to 20 µm, which correspond to an aspect ratio of 15. The fact that the via structures are electrically isolated makes them a suitable start-point to realize interconnections through a wafer. Furthermore, the application field of the via structure is broadened by the flexibility in the design of the structure, which makes it possible to apply an almost arbitrary membrane material onto the via structure at the end of the process.

Suppression of spurious lateral modes in thickness-excited FBAR resonators

Thin film bulk acoustic wave resonators (FBAR) utilize thickness-excited modes in which the resonant frequency is determined by the thickness of the structure and the wave velocity of the mode used. Unfortunately, other resonant modes also may be excited in the device. Some of these correspond to low-frequency, laterally-excited modes arid, although a relatively small amount of the total energy is absorbed by these modes, their harmonics may produce an undesirable response around the fundamental resonance frequency of the desired thickness mode. This work explores various ways of suppressing the spurious effects caused by lateral-excited modes by studying their dependence of the electrode geometry. The origin of the lateral-excited modes is discussed in detail, and the results from a number of different electrode geometries are compared. A new elliptical electrode shape for suppression of spurious modes is developed and demonstrated.

Innovative process development for a new micro-tribosensor using surface micromachining

We present a study on thick Si-rich nitride/polycrystalline Si/silicon oxide multilayer-stacks made by LPCVD and PECVD techniques. The pattern transfer into the multilayer-stacks is achieved by dry etching techniques such as SF6-based ICP plasma and the so-called Bosch processes. The steep profiles and high selectivity obtained for the developed processes allow us to design and fabricate complex MEMS devices which consist of multiple sacrificial and multiple locally doped Si or polycrystalline Si layers. A new etch-stop technique has been developed, which allows accurate stopping on any particular layer with the SF6-based ICP plasma etch process. In order to obtain freestanding structures for tribotesting purposes, the residual stress variation of thick undoped silicon oxide layers (obtained by various methods) has been studied for high temperature processing.

Precise magnetoresistance and Hall resistivity measurements in the diamond anvil cell

An experimental system in combination with a technique for creating samples has been developed for conducting magnetotransport measurements of 3d ferromagnets as a function of temperature and pressure. Polycrystalline Ni0.985O0.015 thin film samples have been manufactured for experiments at zero pressure and in the diamond anvil cell (DAC) such that the contacts are of a predetermined size. This ensures that the placement of the leads in the pressure chamber of the DAC does not affect the quality of the measurement. Magnetoresistance and Hall resistivity measurements are preformed using the van der Pauw technique and the constant current method. The performance of the experimental apparatus is demonstrated by magnetotransport measurements of Ni0.985O0.015 thin films between 285 and 455 K in applied magnetic fields up to 10 T. The change in magnetic resistivity measured in the transverse configuration at zero pressure in the DAC, −0.0162(2) μΩ  cm T−1 at 297 K, is observed to be negative and linear up to t...