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11-13 May 2011, Aix-en-Provence, France 35% (Fig. 12). Finally the side and the edge are not exactly The approach-retract curves (Fig. 9 & 10) show the tip straight, thus changing the beam section shape and also Iy. cantilever deflection in function of the AFM Z piezoelectric position. During the approach, the AFM head goes down on the sample. The tip cantilever does not move until it touches the sample. In effect we observe a flat part on curves point 1 to 5 (Fig. 8). The shift and the absence of this flat part on curves point 6 and 7 indicate that the sample was tilted. After touching the sample, the AFM head approach is compensated by the tip cantilever deflection at point 1 and by the beam deflection at point 7. So at point 1 the slop angle of the curve is about 45° because there is no beam to absorb the tip cantilever deflection which is the same that the AFM head position (after had touched the sample). Conversely at point 7 a part of the AFM head movement is compensated by the beam deflection. So the tip cantilever deflection is lower and the slop angle of the curve is lower than at previous points. From these results, we calculated the force applied by the AFM tip on the beam (F AFM TIP ) and the deflection of beam (∆z beam ). We considered that we measured the Young modulus of the bending part of the beam (i. e. from the beam anchor to the AFM probe contact point). Thus in our model, the beam length depends on where we measured the Young modulus along the beam. From the curve ∆z beam (F AFM TIP) and using the beam design dimensions (400nm width and 1100 nm thickness), we extracted a beam Young's modulus E of 70 GPa (Fig. 11A). This value is much lower than the mean value from the literature, between 130 and 170 GPa depending on measurement methods, crystal orientation and testing devices (bulk, thin film, beam) [7,8,9]. Fig. 11. Extraction of the beam young modulus. A) based on design dimensions. B) based on measured dimensions. Such a difference can be explained by the polysilicon deposition process [10] but the main reason is the difference on the real dimensions of the beam compared to the design. SEM images showed that the HF etching step to release the beam created an over-etching on the edge of the connection pads (Fig. 3) giving them flexibility. Moreover we extracted the accurate dimensions of beams which are thinner and narrower than expected due to fabrication process (polysilicon deposition and etching). Therefore the beam is more flexible, which explains the lower Vpi and Vpo observed previously. The beam length is an important parameter (see eq. 1) but above all the thickness and the width (Fig. 7) are very critical (affecting Iy) (eq. 1). A beam 110nm thinner than designed (- 10%) generates a Young modulus miscalculation higher than Fig. 12. Young modulus miscalculation depending of the beam thickness error. Therefore, taking into account the real beam dimensions obtained by SEM and AFM, we found a beam Young's modulus of 140 GPa (Fig. 11B) ), which is in better agreement with the literature [11,12,13]. We noted the apparent variation of the Young modulus as a function of the distance from the beam anchor, even though the Young modulus is a material property supposed to be constant. This could be due to the influence of the indentation phenomenon and the elastic deformations of the material in our measurement method. To measure the Young modulus of the beam, we measured the absorption of the AFM cantilever deflection by the beam. At the end of the beam, this absorption is mainly due to the beam bending. The indentation phenomenon and the elastic deformations are negligible. On the other end, near the anchor, they are less negligible compared to the beam bending. Thus the total absorption is higher than the absorption due to the beam bending only, so that the beam appears more flexible than in reality, explaining the lower than expected extracted Young modulus. This explains the constant increase of the Young modulus with the distance from the beam anchor. Based on the same principle, we think that the influence of the over-etching is more pronounced near the anchor than at the end of the beam. It makes the beam appear more flexible than expected and therefore underestimation of the Young modulus again. Nevertheless this Young modulus measurement method allowed to improve the beam design and structure with different materials, to study the mechanical reliability of the beam, and is helpful to improve the electromechanical behavior of the NS device. 350 IV. IMPROVEMENT AND PERSPECTIVES AFM electrical characterization of the NS beam is important to better understand what happens at the nano-scale during a switching event. To perform in-situ AFM electromechanical characterization [14,15] we have improved the design of the chip, by routing the electrical signals of the different pads (Source, Gate and Drain) to the edge of the chip in order to observe the beam working without disturbing the AFM tip (Fig. 13). In addition, we have also changed the structure of the beam with the deposition of a thin layer of platinum (Fig. 14) on the pads and on all the sidewalls of the
eam to improve the electrical contacts and to solve the problems of oxidation caused by humidity which disturb and stick beams (the metal wall covering is explained in [4,5]). Thanks to platinum the reliability and the yield of NS devices was clearly improved [5]. 11-13 May 2011, Aix-en-Provence, France ACKNOWLEDGEMENT Samples were fabricated and designed by Stanford University. They were finalized and customized at the Grenoble Up-line Technological Platform (PTA) which is cooperated by CEA & CNRS within the framework of the French Basic Technology Research (BTR) network. This work has been partly supported by the EU through the Network of Excellence NANOFUNCTION FP7/ICT/NoE (95145). The author would like to thank Xavier Mescot, Martin Gri, Remy Lefevre and Xin Xu for their valuable help. REFERENCES Fig. 13. Optical image of the improved design with electrical contacts routed to the edge of the chip. Fig. 14. SEM image showing thin platinum layer coating on the NS side walls to improve the device structure. V. CONCLUSION The NS electrical characterization showed a correct behavior, while highlighting a few problems. A deeper analysis using AFM and SEM techniques showed small differences from the designed structure. NS mechanical properties were investigated and the beam Young's modulus was extracted taking account of the real sample characteristics and dimensions which are relevant. NS structure and design was improved. The reliability has been increased and the electrical behavior was better. Finally this innovative technique of characterization will help us to explore new fields of NEMS [16]. [1] K. Akarvardar, et al., "Analytical Modeling of the Suspended-Gate FET and Design Insights for Low-Power Logic," IEEE Transactions On Electron Devices, vol. 55, no. 1, p. 48, 2008. [2] K. Akarvardar, et al., "Design Considerations for Complementary Nanoelectromechanical Logic Gates," IEDM, pp. 299-302, 2007. [3] S. Chong, et al., "Nanoelectromechanical (NEM) Relays Integrated with CMOS SRAM for Improved Stability and Low Leakage," in ICCAD International Conference on Computer-Aided Design, 2009. [4] D. Lee, et al., "Titanium nitride sidewall stringer process for lateral nanoelectromechanical relays," in MEMS 2010, IEEE 23rd International Conference, Hong Kong, 2010, pp. 456-459. [5] R. Parsa, et al., "Composite Polysilicon-Platinum Lateral Nanoelectromechanical Relays," in 14th Solid-State Sensors, Actuators, and Microsystems Workshop, Hilton Head, South Caroline, 2010, pp. 7- 10. [6] W. C. Young and R. G. Budynas, Roark's Formulas for Stress and Strain, 7th ed., McGraw-Hill, Ed. 2002 . [7] K. R. Virwani, A. P. Malshe, W. F. Schmidt, and D. K. Sood, "Young’s modulus measurements of silicon nanostructures using a scanning probe system: a non-destructive evaluation approach," Smart Materials and Structures, vol. 12, no. 6, pp. 1028-1032, 2003. [8] M. A. Hopcroft, W. D. Nix, and T. W. Kenny, "What is the Young’s Modulus of Silicon," Journal Of Microelectromechanical Systems, vol. 19, no. 2, pp. 229-238, 2010. [9] C. S. Oh, H. J. Lee, S. G. Ko, S. W. Kim, and H. G. Ahn, "Comparison of the Young’s modulus of polysilicon film by tensile testing and nanoindentation," Sensors and Actuators A, no. 117, p. 151–158, 2005. [10] S. Lee, et al., "The effects of post-deposition processes on polysilicon Young's modulus," Journal of micromechanics and microengineering, vol. 8, no. 4, pp. 330-337, 1998. [11] A. San Paulo, J. Bokor, and R. T. Howe, "Mechanical elasticity of single and double clamped silicon nanobeams fabricated by the vapor-liquidsolid method," Applied Physics Letters, no. 87, p. 053111, 2005. [12] J. Wang, Q. A. Huang, and H. Yu, "Young’s modulus of silicon nanoplates at finite temperature," Applied Surface Science, no. 255, p. 2449–2455, 2008. [13] C. H. Cho, "Characterization of Young’s modulus of silicon versus temperature using a ‘‘beam deflection” method with a four-point bending fixture," Current Applied Physics, vol. 9, p. 538–545, 2009. [14] L. Montès, et al., "AFM Measurement of the Piezoelectric Properties of GaN and GaN/AlN/GaN Individual Nanowires," in MRS, San Francisco, 2010. [15] L. Montès, et al., "Enhancing piezoresistivy and piezoelectricity in nanowire devices," in IEEE Nano 2010, 12th Nanowire Research Society Meeting, Seoul, 2010. [16] X. Xu, et al., "An improved AFM cross-sectional method for piezoelectric nanostructures properties investigation: application to GaN nanowires.," Nanotechnology, vol. 22, no. 10, p. 105704, 2011. 351
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COLLECTION OF PAPERS PRESENTED AT T
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III
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V
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Table of Contents Wednesday 11 May
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PANEL DISCUSSION TEXTILE MICROSYSTE
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Friday 13 May SESSION C4: APPLICATI
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SPECIAL SESSION OF BIO-MEMS/NEMS a
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suspended membrane can be pulled to
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most likely due to not yet consider
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that detectors may measure the diff
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2) Cavity width effect To verify th
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Fig.9. Capacitive sensor output, Va
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The anode and cathode are connected
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! TABLE 3 SUMMARY OF SELECTIVITIES
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The fabrication of optical Cap-Wafe
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the glass is polished down in a cos
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Fig. 14. Time history of the envelo
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Y X Fig. 1. Scanning electron mic
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10 3 11-13 May 2011, Aix-en-Proven
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Intenstiy (counts/second) Fig. 1. X
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etween x 2 to L (remember that x 2
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piezoelectric displacement transduc
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Figure 7 Displacement conditions of
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protect the corners from undercut.
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A. Continuous domain Starting from
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Fig. 8. Central finite difference m
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700 11-13 May 2011, Aix-en-Provenc
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o o o o o o o o Check applicability
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C. Identification Results The ident
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The proposed solution for this prob
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teen wire segments of a coil, as in
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As the metallization is too reflect
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B. Implemented die overview A die c
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IN CLK OUT Fig. 16. Probe setup for
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adhesive material with 30μm thickn
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B. Dynamics of Energy Flows For a l
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80˚C. Additionally, we looked into
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The XRD shows a peak above the 2θ
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fibers which define the electric co
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Figure 15. Key board input system.
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ρ = h 2∆α∆T + + E 1h 3 1 +E 2
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In recent years, the pipe flow moni
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As the speed of the rotor increases
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inches silicon wafers which have th
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samples tested in different vacuum
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l c 11-13 May 2011, Aix-en-Provence
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Vp (V) 3,5 3,0 2,5 2,0 1,5 1,0 0,5
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II. MATHEMATICAL MODEL AND NUMERICA
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fluids travel along a curved channe
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measured mixing indices are depicte
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length, which enables them to focus
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however, a rotation for coincidence
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excludes the nature of the fixed bo
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Using the radial and tangential mid
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Now the challenge in data handling
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value of every active channel. Ther
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electrocardiogram. • The heart be
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In our work, we proposed an innovat
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Fig. 8 Concept of the in-home perso
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found that the early-stage diagnosi
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Power monitoring data detected by w
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device consisted of a bimorph canti
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where C others is the capacitance o
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operation, the pressure inside the
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coefficient compatible with the mic
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Variable Description Value Crab-leg
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Membrane weight (mg) Fig. 4. Struct
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So far, the expected major contribu
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al. used a modified LIGA (German ac
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REFERENCES [1] G. Mehta, J. Lee, W.
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followed by titanium (Ti) which sho
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exposure dose, post exposure bake t
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B. Energy Applications Society is f
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Page 366 and 367: grown to sub-confluence were washed
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Nussbaum Dominic 273 O’Hara T. 35
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