Kentaro Totsu

Ultra-miniature fiber-optic pressure sensor using white light interferometry

We have developed a fiber-optic Fabry–Perot interferometric pressure sensor of 125 µm in diameter and a detection system for medical use. A Fabry–Perot cavity is formed at an optical fiber end. A deformation of the diaphragm of the Fabry–Perot cavity induced by pressure varies the cavity length. White light interferometry is used to avoid error and noise caused by bending of the optical fiber and fluctuation of the light source. The reflection light of the sensor cavity is detected by a commercial high-speed spectrometer. A pressure change has been detected by using the developed sensor system. Animal experiments using a goat have been carried out and dynamic pressure changes in the internal pressure of heart and aorta have been successfully monitored.

Gray-scale photolithography using maskless exposure system

Three-dimensional (3D) photoresist patterns of which shape is precisely controlled are fabricated using a gray-scale photolithography. We utilize a maskless exposure system to achieve the precise gray-scale photolithography at low cost. Multilayered exposure patterns digitally generated by the maskless exposure system are superposed on a photoresist-coated substrate layer by layer. Changing the exposure patterns and the exposure parameters such as the exposure time and the scanning speed of the stage of each exposure make the precise control of the profile of UV dose possible. The exposure process does not require any hard masks such as expensive gray-scaled hard masks; therefore, a fabrication of variable 3D patterns at low cost can be achieved, which is an advantage for developing microelectromechanical systems devices. A spherical and an aspherical microlens and its arrayed patterns of 100μm in diameter and 6μm in height are fabricated by a superposition of sixteen-layered exposure patterns. The profil...

Tactile display for 2-D and 3-D shape expression using SMA micro actuators

Tactile display which displays character and graphic information dynamically from computer by making pins array up and down has been developed. Shape Memory Alloy (SMA) micro-coil actuators contract and make the pins up and down when an electrical current is supplied. Magnetic material tube is attached to each pin and a permanent magnet fixes position of the pins up or down. Electrical consumption is low because the current is supplied only when the pins move. A 2-D tactile display which has 100 (10/spl times/10) pins array has been developed and successfully operated. The tactile information were displayed sequentially every 0.3 second and the pins were latched at 0.1 N by magnetic force. The pins are arranged at a pitch of 2.5 mm and move 2 mm up and down individually. In order to present the tactile information accurately, narrower pin pitch of the tactile display is preferable. A module for tactile display with a pin pitch of 1.27 mm has been fabricated and successfully operated. A multi-step magnetic latch has been developed for a 3-D tactile display. By using these mechanisms, large displacement and accurate positioning of the pin for 3-D expression can be realized.

Vacuum sealed ultra miniature fiber-optic pressure sensor using white light interferometry

We have developed a fiber-optic Fabry-Perot interferometer pressure sensor of 125 /spl mu/m in diameter of which cavity is sealed in vacuum. White light interferometry is used to avoid noise caused by bending of the optical fiber and a fluctuation of the light source. The reflection light is measured by high-speed spectrometer. A Fabry-Perot cavity is formed at the optical fiber end. A deformation of the diaphragm induced by pressure varies the cavity length. To avoid influence of temperature change to the sensor output, the cavity is sealed in vacuum. The sensing element is bonded to the optical fiber end by soldering in vacuum. Sn layer is formed on the metal spacer of the sensing element and is bonded to the Cr/Cu/Au layer patterned at the optical fiber end. Cr half-mirror is also patterned at the core of the fiber end for making interferometer. Pressure is successfully monitored in real-time using the sensor system.

Gray-scale lithography using mask-less exposure system

A fabrication process of precisely controlled three-dimensional patterns using a gray-scale lithography is presented. Multi-layered exposure patterns digitally generated by a mask-less exposure system are superposed on a photoresist-coated substrate layer by layer. Changing the exposure patterns and the exposure time of each exposure make the precise control of the profile of ultraviolet dose possible. The mask-less exposure system realizes fabrication of variable three-dimensional patterns at low cost with saving time. Photoresist patterns of spherical and aspherical microlens array of 100 /spl mu/m in each diameter are fabricated. The patterns are successfully transferred into silicon substrates with reactive ion etching.

Development of ballistic hot electron emitter and its applications to parallel processing: active-matrix massive direct-write lithography in vacuum and thin-film deposition in solutions

Abstract. Making the best use of the characteristic features in nanocrystalline Si (nc-Si) ballistic hot electron source, an alternative lithographic technology is presented based on two approaches: physical excitation in vacuum and chemical reduction in solutions. The nc-Si cold cathode is composed of a thin metal film, an nc-Si layer, an n+-Si substrate, and an ohmic back contact. Under a biased condition, energetic electrons are uniformly and directionally emitted through the thin surface electrodes. In vacuum, this emitter is available for active-matrix drive massive parallel lithography. Arrayed 100×100 emitters (each emitting area: 10×10  μm2) are fabricated on a silicon substrate by a conventional planar process, and then every emitter is bonded with the integrated driver using through-silicon-via interconnect technology. Another application is the use of this emitter as an active electrode supplying highly reducing electrons into solutions. A very small amount of metal-salt solutions is dripped onto the nc-Si emitter surface, and the emitter is driven without using any counter electrodes. After the emitter operation, thin metal and elemental semiconductors (Si and Ge) films are uniformly deposited on the emitting surface. Spectroscopic surface and compositional analyses indicate that there are no significant contaminations in deposited thin films.

Active bending ileus tube using shape memory alloy for treatment of intestinal obstruction

Soft and long silicone rubber tube (long intestinal tube; LIT) is commonly used for conservative treatment in intestinal obstruction (ileus). The LIT is inserted into the intestine for depressurization by continuous suction from outside the body. In insertion of the tube, it is difficult to pass the lower opening of the stomach (pylorus) because of its narrowness. An LIT that has stainless steel weights at the tip is most widely used for the insertion. This tube utilizes gravity to facilitate manipulation of the tip. However, a patient must endure pain when he or she changes position. For accurate positioning of the tip, active bending LIT using shape memory alloy (SMA) coil micro actuator, which contracts by supplying electrical current has been developed. The tube consists of a bending tip (external diameter, 6 mm; length, 40 mm) and a 3-m-long silicone rubber tube. It enables easier and more reliable passage at the pylorus. The maximum bending angle was 110 degrees and the bending tip is flexible even if it bends because of softness of the SMA micro-coil. The surface temperature of the tip during active bending motion was measured under conditions of 38/spl deg/C and it takes 45 seconds for the surface temperature to rise over 41/spl deg/C when the bending angle is maintained at 30 degrees.

Piezoelectric 2D microscanner for precise laser treatment in the human body

Laser irradiation in the human body using an optical fiber is an effective method of minimally invasive laser treatment. For realizing precise laser treatment in the human body, a two-dimensional (2D) laser scanning micro tool has been developed. A laser is transmitted through an optical fiber and a micro rod lens. The laser is reflected and scanned by a 2D microscanner and focused on an objective area. The fabricated 2D microscanner has three piezoelectric unimorph cantilevers that have a ball joint at each tip and a mirror. The mirror is supported by a pivot from underside and is inclined by pushing down by three cantilevers on the top of the mirror. The maximum inclined angle of the mirror is 30 degrees. Using potassium-titanyl-phosphate (KTP) laser, a function of the laser scanning is confirmed. For insertion the 2D laser scanning micro tool into a working channel of a conventional endoscope, these components are assembled and packaged into a tube. In the future, this tool can be used not only for laser treatment but also for in vivo microscopic inspection. By combining the 2D microscanner and the microscopic inspection techniques, for example micro confocal laser scanning microscope or Endoscopic Optical Coherence Tomography (EOCT), the tool might be more effective for precise laser treatment.

Free-standing subwavelength grid infrared rejection filter of 90 MM diameter for LPP EUV light source

A subwavelength grid infrared (IR) filter as large as 90 mm in diameter was fabricated and tested on a 6 inch Si wafer for a laser-produced plasma (LPP) extreme ultraviolet (EUV) light source used in the next generation lithography tools. The IR filter is a grid type, which has higher thermal stability compared with a conventional multilayer metal membrane filter. The grid is a free-standing Mo-coated Si honeycomb structure with a thickness of 5 μm, a wire width of only 0.35 μm and a pitch of 4.5 μm. Such a large-size free-standing microstructure was successfully fabricated by carefully balancing film stress at each process step. The fabricated IR filter demonstrated 99.7 % rejection for 10.6 μm IR light.

Development of a MEMS electrostatic condenser lens array for nc-Si surface electron emitters of the Massive Parallel Electron Beam Direct-Write system

Developments of a Micro Electro-Mechanical System (MEMS) electrostatic Condenser Lens Array (CLA) for a Massively Parallel Electron Beam Direct Write (MPEBDW) lithography system are described. The CLA converges parallel electron beams for fine patterning. The structure of the CLA was designed on a basis of analysis by a finite element method (FEM) simulation. The lens was fabricated with precise machining and assembled with a nanocrystalline silicon (nc-Si) electron emitter array as an electron source of MPEBDW. The nc-Si electron emitter has the advantage that a vertical-emitted surface electron beam can be obtained without any extractor electrodes. FEM simulation of electron optics characteristics showed that the size of the electron beam emitted from the electron emitter was reduced to 15% by a radial direction, and the divergence angle is reduced to 1/18.