Midterm report

1. Midterm report Department ：Institute of NEMS Student ID︰d9635808 Report︰ Yen - Liang Lin

2. Outline • Introduction of tactile system • Abstract • Operation principle • Fabrication process • Experimental results • Conclusion • Reference

3. Introduction • The Braille system is a method that is widely used by blind people to read and write. • Each Braille character or cell is made up of six dot positions, arranged in a rectangle containing two columns of three dots each. • Today different Braille codes (or code pages) are used to map character sets of different languages to the six bit cells. • Dot height is approximately 0.02 inches (0.5 mm); the horizontal and vertical spacing between dot centers within a Braille cell is approximately 0.1 inches (2.5 mm). • A standard Braille page is 11 inches by 11.5 inches and typically has a maximum of 40 to 43 Braille cells per line and 25 lines.

4. Introduction – SMA • The SMA (Shape-memory alloy spring) actuator is heated by supplying electrical current • Palm-top sized tactile display • 100 (10 x 10) pins array • The pins are arranged at a pitch of 2.5 mm and move 2 mm up and down • The tactile information are displayed sequentially every 0.3 sec and the pins are latched at 0.1 N by magnetic force T. Matsumga et al., Transducer, 2005

5. Introduction – SMA • Maximum displacement of 30 µm under 4.2 mN load • It can drastically reduce the volume of the system. • However, it has to be improved the actuation method to generate a large force. W. Yoshikawa et al., MEMS, 2006

6. Introduction - electrostatic A. Yamamoto,et al., MEMS, 2006 L. Yobas,et al., MEMS, 2006

8. Abstract • A chip-sized arrayed actuator device has been developed for application to a tactile display. • Each actuator uses a liquid–vapour phase change to drive a microneedle that stimulates receptors in a finger in contact with the array. • The total size of the 3 × 3 arrayed actuator device is 15 × 15 × 1 mm. • The device performance is experimentally evaluated and a large needle displacement (61 μm) is obtained with an input energy of 457 mJ.

9. Operation principle • A change from the liquid to vapour phase yields a huge increase in volume. This means that one can obtain a relatively large stroke using a small amount of liquid. • To transmit tactile information to the finger receptor, an electrical current is applied to the heater to generate a bubble on the surface, which causes the flexible embrane to deform upwards.

10. Specifications • Needle height：This graph shows that the threshold value for skin deformation for receptor recognition was around 100μm in the quasistatic mode. So we chose a needle height of 200 μm for our device design. • Needle pitch：The value of the two-point discrimination threshold was also experimentally investigated, and a pitch value of 3 mm was obtained. • Total device size：We designed the total size to be 15mm× 15 mm × 1.0 mm and arranged the elements in a 3 × 3 array

11. Fabrication – three parts • 40% KOH：anisotropic wet etching • PDMS resin was used as the membrane material. The size and thickness of the PDMS membrane were 2.5 mm square and 20 μm, • Si wafer thickness： 200 µm • Au/Cr heater：The film thickness was 270 nm. • sputtering and lift-off

12. Fabrication – assembly • Liquid sealing into chamber → We chose fluorinert FC-72 (3M Chemicals), which has a low boiling point (56 ◦C). • Photocurable resin (TB3115B,Three Bond) for sealing .The final assembly process was performed in the driving liquid to avoid aeration, • PDMS has high gas permeability, so the bonded structure were coated with the parylene-C film(2~3µm), which has excellent step-coverage properties.

13. Experimental Results • The width and voltage of the applied pulse voltage were 5 ms and 31.25 V, respectively. • The displacement reached a maximum of 27.7 μm after 330 ms and then fell to 2.5 μm. It did not return to the original value even after several seconds. • A laser displacement sensor was placed over the needles and used to detect their displacement by the bubble actuation.

14. Experimental Results • This picture was taken after 1 s. Several bubbles remained in the cavity. These bubbles finally coalesced into one large bubble after 3 s. This single large bubble gradually shrank. • Bubble generation at maximum displacement. A large number of tiny bubbles coming off the heater were observed. • The state before the voltage was applied. No bubbles were observed in this state ※ The coalesced bubble remained after the input voltage was turned off, which makes the response poor.

15. Experimental Results • The needle displacement increases with input energy and does not depend on the pulse wave forms if the input energy is the same. • A large displacement of 60.7μm was obtained for an input energy of 457 mJ (pulse width: 15 ms; amplitude: 28.7 V). • The response time did not depend on the input energy or pulse waveform. The value was 330 ms.

16. Results – Periodic operation • The applied pulse width, amplitude and frequency were 1 ms, 52.2 V and 1 Hz, respectively. • The total displacement gradually increased to the range of 30–48 μm as the number of the periodic motions increased. The motion reached the steady state (thermal equilibrium state) after 8 s from the onset of the driving. • The base value of the periodic motion increased to 30 μm, and the amplitude became nearly 20 μm, in the steady state. • The off-set value (30 μm in this case) must be considered at the device design stage if the device is operated at 1 Hz.

17. Conclusion • The needle height and pitch were chosen to be 200 μm and 3 mm, respectively, considering the skin deformation and two-point discrimination threshold. • The needle displacement produced by bubble generation reached a maximum of 27.7 μm after 330 ms, and then it fell to 2.5 μm. It did not return to the original value even after several seconds because the bubbles remained in the cavity. • The needle displacement increased with input energy and did not depend on the pulse wave forms for the same input energy. A large displacement of 60.7 μm was obtained when the input energy was 457 mJ (pulse width: 15 ms; amplitude: 28.7 V).

18. Reference • Mitsuhiro Shikida, Tsubasa Imamura, Shinji Ukai, Takaaki Miyajiand Kazuo Sato, “Bubble Driven Arrayed Actuator Device for a Tactile Display,” Transducer, 2007. • Mitsuhiro Shikida, Tsubasa Imamura, Shinji Ukai, Takaaki Miyajiand Kazuo Sato, “Fabrication of a bubble-driven arrayedactuator for a tactile display,” J. of Micromech. Microeng., 18, 065012(9pp), 2008. • T. Matsumgal, W. Makishi, K. Totsu, M. Esashi and Y. Haga, “2-D and 3-D Tactile Pin Display Using SMA Micro-coil Actuator and Magnetic Latch,” Transducer, 2007. • W.Yoshikawa, A.Sasabe, K.Sugano, T.Tsuchiya, O.Tabata and A.Ishida, “Vertical drive micro actuator using SMA thin film for a smart button,” MEMS, 2006. • L. Yobas, D. M. Durand, G. G. Skebe, F. J. Lisy, M.l A. Huff,” A Novel Integrable Microvalve for Refreshable Braille Display System,” Journal of microelectromechanical systems., 12 , pp252-263 , 2003. • A. Yamamoto, T. Ishii, and T. Higuchi, “Electrostatic tactile display for presenting surface roughness sensation,” IClT , 2003.

19. Thank you for your attention !