This is part I of a series of two papers dedicated to the presentation of a novel, large throughput, experimental procedure to determine the three-dimensional distribution of the etch rate of silicon in a wide range of anisotropic etchants, including a total of 30 different etching conditions in KOH, KOH+IPA, TMAH and TMAH+Triton solutions at various concentrations and temperatures. The method is based on the use of previously reported, vertically micromachined wagon wheels (WWs) (Wind and Hines 2000 Surf. Sci. 460 21-38; Nguyen and Elwenspoek 2007 J. Electrochem. Soc. 154 D684-91), focusing on speeding up the etch rate extraction process for each WW by combining macrophotography and image processing procedures. The proposed procedure positions the WWs as a realistic alternative to the traditional hemispherical specimen. The obtained, extensive etch rate database is used to perform wet etching simulations of advanced systems, showing good agreement with the experimental counterparts. In part II of this series (Gosálvez et al J. Micromech. Microeng. 21 125008), we provide a theoretical analysis of the etched spoke shapes, a detailed comparison to the etch rates from previous studies and a self-consistency study of the measured etch rates against maximum theoretical values derived from the spoke shape analysis.
We evaluated the effective transverse piezoelectric coefficients (e 31,f ) of Pb(Zr,Ti)O 3 (PZT) thin films from both the direct and converse piezoelectric effects of unimorph cantilevers. (001) preferentially oriented polycrystalline PZT thin films and (001)/(100) epitaxial PZT thin films were deposited on (111)Pt/Ti/Si and (001)Pt/MgO substrates, respectively, by rf-magnetron sputtering, and their piezoelectric responses owing to intrinsic and extrinsic effects were examined. The direct and converse je 31,f j values of the polycrystalline PZT thin films were calculated as 6.4 and 11.5-15.0 C/m 2 , respectively, whereas those of the epitaxial PZT thin films were calculated as 3.4 and 4.6-4.8 C/m 2 , respectively. The large je 31,f j of the converse piezoelectric property of the polycrystalline PZT thin films is attributed to extrinsic piezoelectric effects. Furthermore, the polycrystalline PZT thin films show a clear nonlinear piezoelectric contribution, which is the same as the Rayleigh-like behavior reported in bulk PZT. In contrast, the epitaxial PZT thin films on the MgO substrate show a piezoelectric response owing to the intrinsic and linear extrinsic effects, and no nonlinear contribution was observed.
In this work, the orientation-dependent adsorption of surfactant molecules on the silicon surface during etching in surfactant-added tetramethylammonium hydroxide (TMAH) is investigated. Triton X-100 (C14H22O(C2H4O)n, n = 9–10) and 25 wt% TMAH are used as surfactant and main etchant, respectively. The crystallographic planes affected by the surfactant molecules are determined by analyzing the etching behavior of different mask patterns on Si{1 0 0} wafers and silicon hemispheres in pure and surfactant-added TMAH. Taken together, the shapes of the etched profiles and the analysis of the hemispherical etch rates confirm that thick and dense adsorbed surfactant layers are typically formed on both the exact and vicinal Si{1 1 0} surfaces. In addition, the results indicate that the adsorbed surfactant layer behaves as a permeable mask, partially slowing down the etch rate of the affected surface orientation/s and thus enforcing their appearance on the etching front. The peculiar etching properties of surfactant-added and surfactant-free TMAH are then utilized for the fabrication of advanced micromechanical structures with new shapes on Si{1 0 0} wafers and polydimethylsiloxane based on complex Si{1 0 0} molds.
We have fabricated a simple Si-MEMS device consisting of a microcantilever and a base to measure active tension generated by skeletal muscle myotubes derived from murine myoblast cell line C2C12. We have developed a fabrication process for integration of myotubes onto the device. To position myotubes over the gap between the cantilever and the base without damage due to mechanical peeling or the use of an enzymatic reaction, we cultured myotubes on poly-N-isopropylacrylamide (PNIPAAm) as a sacrifice layer. By means of immune staining of alpha-actinin, it was confirmed that a myotube micropatterned onto the device bridged the gap between the cantilever and the base. After 7d differentiation, the myotube was actuated by electrical stimulation. The active tension generated by the myotube was evaluated by measuring the bending of the cantilever using image processing. On twitch stimulation, the myotube on the device contracted and generated active tension in response to the electrical signals. On tetanus tension measurement, approximately 1.0 microN per single myotube was obtained. The device developed here can be used in wide area of in vitro skeletal muscle studies, such as drug screening, physiology, regenerative medicine, etc.
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