An electrostatically latched and magnetically ... - Semantic Scholar
IEICE Electronics Express, Vol.3, No.5, 87–91
An electrostatically latched and magnetically erased MEMS re-writable bitmap image display R. Shigematsu1a) , A. Higo1,2 , H. Toshiyoshi1,2 , and H. Fujita1 1
Institute of Industrial Science, The University of Tokyo,
4–6–1 Komaba, Meguro-ku, Tokyo 153–8505, Japan 2
Kanagawa Academy of Science and Technology,
3–2–1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa 213–0012, Japan a) [email protected]
Abstract: We propose a new type of re-writable bitmap image display component using the MEMS (Micro Electro Mechanical Systems) -controlled light scattering. The device is made of a light-guided transparent substrate (glass) and a thin sheet of semi-transparent plastic film (PDMS; Poly Di Methyl Siloxane) with magnetic nickel and light– diffusing glass powders formed in an electrostatic parallel-plate actuator. The membrane segment under a moderate drive voltage (110 V), is designed to suspend itself at the rest position over the glass substrate, in which an illumination light travels at the condition of internal total reflection. When an extra force is applied for instance, by manually pressing with a glass rod (diameter 1 mm), the membrane is electrostatically brought into contact with the glass substrate, where the light scatters through the membrane to the eyes of a viewer. The trace of the glass-rod stroke persists in the membrane as long as the driving voltage is applied. The image can also be partially erased by magnetically pulling up the magnetic membrane using a tiny permanent magnet scanned over the device. In other words, the developed device has a function of blackboard to which the bitmap image data is written manually. Thanks to the simplicity of the structure and operation principle, the device can be made in large area by the recent “Large Area MEMS” such as a roll-to-roll printing, inkjet printing and plastic molding. Keywords: display, electronic paper, optical MEMS, plastic MEMS, actuator, blackboard Classification: Micro- or nano-electromechanical systems References
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
[1] T. M¨ akel¨a, S. Jussila, M. Vilkman, H. Kosonen, and R. Korhonen, “Rollto-roll method for producing polyaniline patterns on paper,” Synthetic Metals, vol. 135–136, pp. 41–42, 2003.
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IEICE Electronics Express, Vol.3, No.5, 87–91
[2] S. Fuller, E. Wilhelm, and J. Jacobson, “Ink-jet printed nanoparticle microelectromechanical systems,” J. Microelectromech. Syst., vol. 11, no. 1, pp. 54–60, Feb. 2002. [3] P. F. van Kessel, L. J. Hornbeck, R. E. Meier, and M. R. Douglass, “A MEMS-Based Projection Display,” Proc. IEEE, vol. 86, no. 8, pp. 1687– 1704, 1998. [4] D. T. Amm and R. W. Corrigan, “Grating Light Valve Technology: Update and Novel Applications,” SID International Symposium Digest of Technical Papers, pp. 29–32, 1998. [5] T. Oguchi, M. Hayase, and T. Hatsuzawa, “Micromachined display device using sheet waveguide and multicantilevers driven by electrostatic force,” IEEE Trans. Ind. Electron., vol. 52, no. 4, pp. 984–991, Aug. 2005.
1
Introduction
Smallness and high precision have been the first priority advantage that the MEMS (micro electro mechanical systems) can deliver in the last decades. In contrast to this approach, a concept of large area MEMS has been proposed to develop relatively large system in a meter-scale still with the micron-scale resolution using the processing techniques such as roll-to-roll printing [1], ink-jet printing [2], and plastic molding. With this emerging manufacturing technique, we foresee new electronic devices and systems such as image displays. Unlike the conventional MEMS displays that use micro mirror or gratings spatial light modulation (SLM) [3, 4], in this paper, we present a totally new idea of image displays that could be used like an electronic version of blackboards, on which one can draw and erase arbitrary shapes and images. The bitmap matrix consists of an arrayed light spot where the light is scattered from a physical material contact on a planar light waveguide. In older to realize the full function of the blackboard such as drawing, selfholding, partial and entire erasing, we used the combination of electrostatic and magnetic micro actuation principle; the electrostatic pull-in force is used to hold the pixel membrane at the ON-state, and magnetic attraction force is to pull-up the membrane to the OFF-state. This paper reports the principle and the first successful demonstration of such MEMS blackboard displays.
2
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
Design of MEMS Re-writable Color Pixel Array
A semi-transparent membrane covers a waveguide glass substrate with a small air gap separated by a spacer grid. Each of the membrane and the waveguide substrate has a conductive layer for electrostatic attraction. A transmitting light is coupled from one side of the substrate; it travels inside at the condition of the internal total reflection due to the difference of the refractive index between the air and the substrate. Therefore, the traveling light does not go out from the substrate when the membrane is separated by the air gap. On the other hand, the light scatters and diffuses in the membrane, when
88
IEICE Electronics Express, Vol.3, No.5, 87–91
it is brought into mechanical contact upon the substrate by the electrostatic operation [5]. The layered structure of the membrane and the substrate is shown in Fig. 1. The membrane can be actuated by electrostatic force and magnetic force in a cooperative manner; the membrane is made of an electrical insulating layer of PEN (poly ethylene naphthalate), electrical conduction layer of ITO (indium tin oxide) and a magnetically attractable layer with nickel micro particles suspended in a spun-on PDMS (poly dimethyl siloxane). We also mixed micro particles of silica glass for better visibility by optical scattering and diffusion effects. Typical weight ratio of nickel, glass and PDMS was 1 : 1 : 1.
Fig. 1. Schematic composition of “an electrostatically latched and magnetically erased MEMS rewritable bitmap image display”. The device consists of transparent membrane and substrate. A transmitting light is given from one side and a voltage is applied between the electrodes.
On the waveguide substrate, we formed an ITO electrode and a spacer made of SU-8 photoresist (32 µm in height) and an underlying aluminum layer of the line shape for better adhesion and for better shield of stray light.
3
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
Principle and Experiment
Figure 2 shows the actuation principle of the MEMS re-writable pixel, which copies the function of the blackboard, namely, writing, partial erase and entire erase. At the initial state, a constant voltage is applied between the membrane and the substrate such that the membrane would not be brought into contact with the substrate; all the pixels are at the dark mode. For writing, one gives an additional force to the membrane by, for instance, pressing it and the membrane segment is pulled-in to the substrate, where the pixels becomes bright by scattering. Partial erase is possible by pulling up the
89
IEICE Electronics Express, Vol.3, No.5, 87–91
Fig. 2. Diagram of pixel ON/OFF operation. (a) Initial state. (b) Pixels are forced to deform manually. (c) Pixels can be locally turned off by being pulled with magnetic force. (d) All pixels can be simultaneously turned off by releasing the applying voltage.
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
membrane with a permanent magnet, by which the pixel becomes dark again. To erase the bright pixels at a time, one may remove the drive voltage. At first, we changed the voltage to implement the bi-stable condition of the membrane. We first increased the bias voltage gradually and we observed the membrane spontaneously brought into contact at 140 Volt without additional external force applied. While decreasing the voltage from 140 Volt, the contact area became small gradually. At 110 Volt, the bright area of a pixel was 25%. The membrane was released at 72 Volt, where the restoring force of the membrane exceeded the electrostatic attraction. This means that a bias voltage in the range between 72 Volt and 140 Volt enables us to operate the device at the bi-stable condition (dark and bright) with an aid of small external force. Figure 3 shows pixels in operation (movie file attached). Nine pixels are observerd from the device top with an optical microscope with a color CCD camera. A photoresist pattern of 2 mm in pitch and 20 µm in width was seen though the semi-transparent membrane. In this operation, we gave a bias voltage of 110 Volt to the device, and manually pressed the pixels with a small glass rod (diameter 1 mm) to turn the pixel on one by one. The observed pixels were bright and clearly visible in a bright room. The movie shows 8 pixels were turned on, and partially erased using a permanent magnet
90
IEICE Electronics Express, Vol.3, No.5, 87–91
Fig. 3. Operation of the device (movie attached). After pushing some pixels down selectively, pulled the membrane back by a magnet. Finally erased all pixels by releasing the applying voltage. (Co5 Sm, 0.35 T, 5 mm*5 mm*3 mmt , weight 0.65 g). Finally, we released the voltage, and the pixels were all turned off at a time. In conclusion, we proposed and demonstrated “an electrostatically latched and magnetically erased MEMS re-writable bitmap image display” using a new actuationsequence of an electrostatic actuator; “manual pull-in” and “magnetic pull-up”; and its application for a blackboard type large display. In addition, the device consists of so simple layered structures that it is compatible with “Large Area MEMS” technologies.
Acknowledgements We thank T. Taii, M. Mita, T. Ishida, K. Takahashi and E. Sarajaric for experimental support and discussion. We thank Teijin DuPont Films Japan Limited for providing us with the PEN films used in this work.
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
91
An electrostatically latched and magnetically erased MEMS re-writable bitmap image display R. Shigematsu1a) , A. Higo1,2 , H. Toshiyoshi1,2 , and H. Fujita1 1
Institute of Industrial Science, The University of Tokyo,
4–6–1 Komaba, Meguro-ku, Tokyo 153–8505, Japan 2
Kanagawa Academy of Science and Technology,
3–2–1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa 213–0012, Japan a) [email protected]
Abstract: We propose a new type of re-writable bitmap image display component using the MEMS (Micro Electro Mechanical Systems) -controlled light scattering. The device is made of a light-guided transparent substrate (glass) and a thin sheet of semi-transparent plastic film (PDMS; Poly Di Methyl Siloxane) with magnetic nickel and light– diffusing glass powders formed in an electrostatic parallel-plate actuator. The membrane segment under a moderate drive voltage (110 V), is designed to suspend itself at the rest position over the glass substrate, in which an illumination light travels at the condition of internal total reflection. When an extra force is applied for instance, by manually pressing with a glass rod (diameter 1 mm), the membrane is electrostatically brought into contact with the glass substrate, where the light scatters through the membrane to the eyes of a viewer. The trace of the glass-rod stroke persists in the membrane as long as the driving voltage is applied. The image can also be partially erased by magnetically pulling up the magnetic membrane using a tiny permanent magnet scanned over the device. In other words, the developed device has a function of blackboard to which the bitmap image data is written manually. Thanks to the simplicity of the structure and operation principle, the device can be made in large area by the recent “Large Area MEMS” such as a roll-to-roll printing, inkjet printing and plastic molding. Keywords: display, electronic paper, optical MEMS, plastic MEMS, actuator, blackboard Classification: Micro- or nano-electromechanical systems References
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
[1] T. M¨ akel¨a, S. Jussila, M. Vilkman, H. Kosonen, and R. Korhonen, “Rollto-roll method for producing polyaniline patterns on paper,” Synthetic Metals, vol. 135–136, pp. 41–42, 2003.
87
IEICE Electronics Express, Vol.3, No.5, 87–91
[2] S. Fuller, E. Wilhelm, and J. Jacobson, “Ink-jet printed nanoparticle microelectromechanical systems,” J. Microelectromech. Syst., vol. 11, no. 1, pp. 54–60, Feb. 2002. [3] P. F. van Kessel, L. J. Hornbeck, R. E. Meier, and M. R. Douglass, “A MEMS-Based Projection Display,” Proc. IEEE, vol. 86, no. 8, pp. 1687– 1704, 1998. [4] D. T. Amm and R. W. Corrigan, “Grating Light Valve Technology: Update and Novel Applications,” SID International Symposium Digest of Technical Papers, pp. 29–32, 1998. [5] T. Oguchi, M. Hayase, and T. Hatsuzawa, “Micromachined display device using sheet waveguide and multicantilevers driven by electrostatic force,” IEEE Trans. Ind. Electron., vol. 52, no. 4, pp. 984–991, Aug. 2005.
1
Introduction
Smallness and high precision have been the first priority advantage that the MEMS (micro electro mechanical systems) can deliver in the last decades. In contrast to this approach, a concept of large area MEMS has been proposed to develop relatively large system in a meter-scale still with the micron-scale resolution using the processing techniques such as roll-to-roll printing [1], ink-jet printing [2], and plastic molding. With this emerging manufacturing technique, we foresee new electronic devices and systems such as image displays. Unlike the conventional MEMS displays that use micro mirror or gratings spatial light modulation (SLM) [3, 4], in this paper, we present a totally new idea of image displays that could be used like an electronic version of blackboards, on which one can draw and erase arbitrary shapes and images. The bitmap matrix consists of an arrayed light spot where the light is scattered from a physical material contact on a planar light waveguide. In older to realize the full function of the blackboard such as drawing, selfholding, partial and entire erasing, we used the combination of electrostatic and magnetic micro actuation principle; the electrostatic pull-in force is used to hold the pixel membrane at the ON-state, and magnetic attraction force is to pull-up the membrane to the OFF-state. This paper reports the principle and the first successful demonstration of such MEMS blackboard displays.
2
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
Design of MEMS Re-writable Color Pixel Array
A semi-transparent membrane covers a waveguide glass substrate with a small air gap separated by a spacer grid. Each of the membrane and the waveguide substrate has a conductive layer for electrostatic attraction. A transmitting light is coupled from one side of the substrate; it travels inside at the condition of the internal total reflection due to the difference of the refractive index between the air and the substrate. Therefore, the traveling light does not go out from the substrate when the membrane is separated by the air gap. On the other hand, the light scatters and diffuses in the membrane, when
88
IEICE Electronics Express, Vol.3, No.5, 87–91
it is brought into mechanical contact upon the substrate by the electrostatic operation [5]. The layered structure of the membrane and the substrate is shown in Fig. 1. The membrane can be actuated by electrostatic force and magnetic force in a cooperative manner; the membrane is made of an electrical insulating layer of PEN (poly ethylene naphthalate), electrical conduction layer of ITO (indium tin oxide) and a magnetically attractable layer with nickel micro particles suspended in a spun-on PDMS (poly dimethyl siloxane). We also mixed micro particles of silica glass for better visibility by optical scattering and diffusion effects. Typical weight ratio of nickel, glass and PDMS was 1 : 1 : 1.
Fig. 1. Schematic composition of “an electrostatically latched and magnetically erased MEMS rewritable bitmap image display”. The device consists of transparent membrane and substrate. A transmitting light is given from one side and a voltage is applied between the electrodes.
On the waveguide substrate, we formed an ITO electrode and a spacer made of SU-8 photoresist (32 µm in height) and an underlying aluminum layer of the line shape for better adhesion and for better shield of stray light.
3
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
Principle and Experiment
Figure 2 shows the actuation principle of the MEMS re-writable pixel, which copies the function of the blackboard, namely, writing, partial erase and entire erase. At the initial state, a constant voltage is applied between the membrane and the substrate such that the membrane would not be brought into contact with the substrate; all the pixels are at the dark mode. For writing, one gives an additional force to the membrane by, for instance, pressing it and the membrane segment is pulled-in to the substrate, where the pixels becomes bright by scattering. Partial erase is possible by pulling up the
89
IEICE Electronics Express, Vol.3, No.5, 87–91
Fig. 2. Diagram of pixel ON/OFF operation. (a) Initial state. (b) Pixels are forced to deform manually. (c) Pixels can be locally turned off by being pulled with magnetic force. (d) All pixels can be simultaneously turned off by releasing the applying voltage.
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
membrane with a permanent magnet, by which the pixel becomes dark again. To erase the bright pixels at a time, one may remove the drive voltage. At first, we changed the voltage to implement the bi-stable condition of the membrane. We first increased the bias voltage gradually and we observed the membrane spontaneously brought into contact at 140 Volt without additional external force applied. While decreasing the voltage from 140 Volt, the contact area became small gradually. At 110 Volt, the bright area of a pixel was 25%. The membrane was released at 72 Volt, where the restoring force of the membrane exceeded the electrostatic attraction. This means that a bias voltage in the range between 72 Volt and 140 Volt enables us to operate the device at the bi-stable condition (dark and bright) with an aid of small external force. Figure 3 shows pixels in operation (movie file attached). Nine pixels are observerd from the device top with an optical microscope with a color CCD camera. A photoresist pattern of 2 mm in pitch and 20 µm in width was seen though the semi-transparent membrane. In this operation, we gave a bias voltage of 110 Volt to the device, and manually pressed the pixels with a small glass rod (diameter 1 mm) to turn the pixel on one by one. The observed pixels were bright and clearly visible in a bright room. The movie shows 8 pixels were turned on, and partially erased using a permanent magnet
90
IEICE Electronics Express, Vol.3, No.5, 87–91
Fig. 3. Operation of the device (movie attached). After pushing some pixels down selectively, pulled the membrane back by a magnet. Finally erased all pixels by releasing the applying voltage. (Co5 Sm, 0.35 T, 5 mm*5 mm*3 mmt , weight 0.65 g). Finally, we released the voltage, and the pixels were all turned off at a time. In conclusion, we proposed and demonstrated “an electrostatically latched and magnetically erased MEMS re-writable bitmap image display” using a new actuationsequence of an electrostatic actuator; “manual pull-in” and “magnetic pull-up”; and its application for a blackboard type large display. In addition, the device consists of so simple layered structures that it is compatible with “Large Area MEMS” technologies.
Acknowledgements We thank T. Taii, M. Mita, T. Ishida, K. Takahashi and E. Sarajaric for experimental support and discussion. We thank Teijin DuPont Films Japan Limited for providing us with the PEN films used in this work.
c
IEICE 2006
DOI: 10.1587/elex.3.87 Received January 25, 2006 Accepted February 14, 2006 Published March 10, 2006
91
