Advent in 1980s, MEMS(micro-electromechanical Systems) has been under research and development at various Universities and enterprises throughout the world. To meet present industrial requirements, RIMST(Research Institute for Microsystem Technology) in Ritsumeikan University is combining designs, micro-fabrication and material evaluation by establishing microprocess equipment at Microsystem center and Synchrotron Radiation light source at SR center. Under the activities assigned for RIMST, Micro Nano Integrated Device Lab. consists of research on Micro/Nano Science Integrated System as 21st century COE program by the ministry of Education, Culture, Sports, Science and Technology.

Research at Micro Nano Intergrated Devices Lab. is mainly about MEMS devices and LIGA. From Integrated Circuit(IC) technology to micromachining technology, mechanical and electrical systems are combined. Sensors and Actuators are sensing and driving parts of MEMS devices. The development of microprocess technology and fabricating microdevices are our works.

The output of MEMS is to create intelligent microdevices that can process or transduce energy from physical, mechanical, optical, chemical and biological forms as inputs, using microfabrication techniques expanding from IC technology. Our research group is archieving many practical results for sensors, actuators, and process technology by the colaboration with industries.

  
     
 
 
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  Ni-Fe ELECTROPLATING TECHNOLOGY
  
 

LIGA (Lithographic Galvonoformung Abformung) process is an effective technology for reaching high-aspect ratio micro/nano structure. By exposing Synchrotron Radiation to the resist through X-ray mask, the resist will be shaped by X-ray lithography. Micromold will be formed by electroplating metals. The mold will finally be used for batch fabrication of plastic, ceramics or other materials of micro/nano structure.

 
 
 
MICRONEEDLE
  
 
Partly LIGA processing, microneedle array with a novel 3-D shape was fabricated. PCT (Plain-pattern to Cross-section Trsansfer) Technique has been introduced by our research institute. The 2-D pattern on X-ray mask transfers to 3-D structure on PMMA. Tip size can be reduced by tilting mask-angle. The optimized tilting angle has been investigated to reach nanoscaled actual tip-size. Biomedical application is our aim of making the microneedle. The needles is developed for both by drug delivery system and blood extraction system.The improvement of microneedle shape has been done with several mask patterns.

Without fabrication of holes, alternative method of utilizing microneedle as for blood extraction system has been investigated. By the capillary force, microneedle with quadruple-tips can be inserted through skin. Molding process by electroplating is also employed, known as LIGA process.
 
 
LIGA ACTUATOR
 
 


In this work, fabrication of electrostatic microactuators as an application of the LIGA process has been investigated by using a compact synchrotron radiation source "AURORA". So far, there are many reports about microactuators fabricated by surfacemicromachining. The height of the microactuators is limited to about 1 to 10 micrometer in surfacemicromachining. However, the LIGA process can fabricate high aspect ratio microactuators with height of more than 100 micrometer.

The roughness of sidewalls is an important factor for the performance of high aspect ratio microstructures. The sidewall roughness of the Ni microstructure was measured by atomic force microscope (AFM). The peak to valley in the measurement area was 651 nanometer, which was equal to the roughness of the absorber sidewall. The vertical average roughness of the sidewall was 23.1 nanometer. It can be considered as the real finish roughness of the deep X-ray lithography.

The structure of microactuator composed of 100 micrometer high Ni microstructures, a seed layer for electroforming, an isolation layer of 3 micrometer thick SiO2, and a Si wafer. The Ni microstructures act a movable electrode, fixed electrodes, a spring beam and an anchor portion. The movable electrode is separated from the substrate by sacrificial layer etching of the SiO2. SEM photo(upper) shows a wobble motor with 1 millimeter diameter, 100 micrometer height, 2 micrometer minimum width and gap, and then maximum aspect ratio of 50 after Ni electroforming. These microactuators can be applied to high accuracy positioning actuators
 
 
LIGA OPTICAL DEVICES
  
 
Using the same technique as microneedle array, PMMA microlens array having free curved surface has been fabricated ny PCT process. The diameter of each lens is 5 microns to 1mm. Shape of lens is non spherical surfaces. Pitch between each lens is 5 mm. The array is on the maximum chip size of 3 mm.

 
 
PIEZOELECTRIC DEVICE APPLICATIONS
  
 

Recently, a miniaturization and highly efficient actuators are progressing in various fields. In the field of the fluidic systems at present, the miniaturization of systems is useful for bio-MEMS applications. In this research, the aim is developing the micro valve used for a small measurement system which the volumn of air control is needed. There are various types of actuators currently used for the microvalves. A Bimorph shape memory alloy is used in order to open and close the valve by overheating and cooling. The low frequency is required. Usually the electromagnetic actuator is giving a large distance in each response but piezoelectric actuator has a quick response and is easy to miniaturize. Therefore, design and development of the micro valve using bimorph PZT actuator is performed. The piezoelectric ceramic is expanded by applied voltage. The 2 layers of piezoelectric ceramics made the direction of polarization reversible. After the calculation using the theory of Bernouilli's equation as a regular flow of incompressibility and non-viscosity fluid, the experiment value at 98% of the theoretical value was obtained.

 

  
  MICROGYROSCOPE  
 

The development of a dual axis gas gyroscope whose working principle based on the thermo-resistive effect of silicon-hotwire is presented. The proposed gas gyroscope has no moving mass, therefore it can eliminate the inherent problems which usually occur in vibrating gyroscopes. The sensor configuration consists of a piezoelectric pump and a micro thermal sensing element, packaged in an aluminum case with diameter and length of 14mm and 25mm, respectively. The micro sensing element is formed by four silicon thermistor wires, each has dimension of 400?4?2?m3, (L?W?T), are arranged in a square-frame shape. Neon is used for the gas flow inside the sensor case, since it is an inert gas with high thermal conductivity. The sensing element has been fabricated from SOI (silicon on insulator) wafer by conventional MEMS processes. The gyroscope was calibrated by using a turntable, and the measured sensitivity was 0.15mV/deg/sec, which is 62 times larger than that of the gas gyroscope with the same design but using tungsten as sensing element.

The structure of the micro gyroscope is shown in figure above. The micro gyroscope consists of a cross-shaped and folded silicon beam with p-type Si piezoresistors, and pillars at the center and both sides of the beam. The cross-shaped and folded silicon beam is 50 mm - wide and 50 mm- thick. These piezoresistors are formed at the locations where the maximum compressive and tensile stresses are applied. The design of the micro gyroscope is based on the Coriolis effect. The micro gyroscope uses the rotary movement of pillars induced by the four electromagnetic actuators. When the angular rate is applied to the micro gyroscope, the Coriolis force changes the stress in the beam. The micro gyroscope detects the change of stress in the beam via the piezoresistors. The influence of acceleration can be removed by the combination of the configuration of both side pillars and thb bridge circuit.
  
   
 
 
RECIPROCATING ENGINE
 
 


A resonant micro reciprocating engine was designed for electric power generation. Adopting hydrogen gas as a fuel and silicon as a structural material, the theoretical electric power was found to be about 40mW under the conditions that compression ratio is 5, the maximum combustion temperature is 850K, and natural frequency of the piston-spring system is 610Hz. The fabrication process based on ICP-RIE bulk micromachining for micro engine was established and classified into two items: piston and cylinder case(I), packaging of piston and cylinder case and top glass plate(II). The engine operation was demonstrated based on air cycle.

 
 
THERMOPILE
  
 

A thermopile without a membrane and having self-standing structure is proposed in order to realize ideal higher thermal isolation. The proposed structure has two advantages; the absorbed heat transfers from hot contacts to cold contacts only through the thermopile and no heat transfer will occur between the hot and cold contacts, and the heat absorber area can be increased more than the chip area. As a consequence, temperature difference between the hot and cold contacts approaches the ideal value. In this paper, design, fabrication and characteristics of the self-standing polysilicon-metal junction thermopile for an accessory micro power generator are reported, especially focusing on the first advantage.

The thermocouple is composed of an n - type polysilicon and an Au junction. The thermopile was fabricated by MICS (Micromachine Integrated Chip Service: three polysilicon layer structure) organized by the Cooperative Research Committee for Standardization of Micromachines in IEE of Japan.

 
The experimental results of the Seebeck voltage of the thermopile (N =10 thermocouples). A black body plate having uniform typical human skin temperature (307K) was used as the radiation source. Seebeck voltage of more than 6.2mV was obtained. The experimental results are in reasonable agreement with the theoretical calculation. The prospect for application of the thermopile to an accessory micro power generator was shown. In future work, a thermopile with an upper heat absorber will be fabricated and characterized.
 
 
 
NANOMACHINING SENSOR
  
 

 

Silicon nano wires have been studied from the viewpoint of a mechanical sensor application. Polycrystalline silicon (poly-Si) nano wire piezoresistors were fabricated by the electron beam (EB) direct writing and RIE processes. Electrical and electro-mechanical (piezoresistive effect) characteristics of the poly-Si nano wire piezoresistors were investigated in order to verify abilities as sensing elements of mechanical sensors. The poly-Si nano wire piezoresistor was realized by the combination of the electron beam (EB) direct writing and RIE processes. Electrodes were fabricated by Al vacuum evaporation and photolithography.
 

 

  
 
FORCE-MOMENT SENSOR
 
 
 
The design concept and theoretical investigation of a micro multi-axis force-moment sensor utilizing the piezoresistive effect in silicon are introduced. This sensor will be applied in experiments to measure the force and moment acting on boundary particles in a turbulent liquid flow. The sensor is designed to independently detect 3 components of force and 3 components of moment. Conventional and four-terminal piezoresistors have been combined in a single sensing chip.

The model of sensing chip was analyzed by FEM to investigate the stress field in the structure, and to refine the specifications of the beam dimensions. The final dimensions of each arm of the crossbeam are 500 x 120 x 40 m3.

The output characteristics and the sensitivity have been thoroughly analyzed. Total number of piezoresistors is fewer than that of the prior art piezoresistive-based 6-DOF micro force sensors.

The sensing chip is a crossbeam with piezoresistors on the upper surface. The test particle has a diameter of 8mm and is made of polyethylene. Its centroid will coincide with the center of the surface of the crossbeam to minimize the moment induced by horizontal force components. Forces and/or moments acting on the test particle will be transmitted to the sensing chip via a force transmission pillar placed at the center of the sensing chip.
 
 
 
MICROCONNECTOR
  
 

This study focuses on fabrication of micro connectors by combining UV thick resist photolithography and Ni electroforming. This fabrication method is expected to realize high precision micro connectors and high packaging density in mass production.

A fork-type micro connector with high aspect ratio and high packaging density was fabricated using UV thick photoresist and Ni electroforming. A negative photoresist (THB-130N) was used as a mold of Ni electroforming. The tips of socket terminal of the micro connector were formed as movable portions using Cu sacrificial layer etching. In order to make firm contact of the micro connector, two-step guidance was adopted. The size of the terminal of fabricated micro connector was 50 mm- thickness and 15 mm-width (minimum). The maximum aspect ratio of the fabricated micro connector is 3.3 and the terminal pitch is 80 mm. Figure 1 shows SEM photograph of the socket terminal which was formed by the Ni electroforming. A contact resistance of a 50 mW,a contact force of 2.08mN,Young痴 modulus of 80 GPa and a permissible current of 400 mA (single pair of the plug and socket terminals) were obtained practicl use for the micro connector.

 
 
 
BIO-DEVICES
  
 

A new method of using silicon microneedle array in Bio-Medical applications is introduced in this work. The hollow microneedle array with the facilitation of an insertion guide array have been designed and fabricated. The needles can be pushed down through the second layer of human skin with less-bending. The tip of microneedle will be led by the insertion guide to pierce the skin perpendicularly. The silicon bulk micromachining technique using an inductively coupled plasma (ICP) etcher has been employed to fabricate the microneedle array and the insertion guide array. The array chips are 5x5 mm2 for both structures. The needle array chip contains 100 microneedles with 100um and 30um of the outer diameter and the hole diameter respectively. The guide array chip is 100 um-thick and contains 100 guiding holes with 120 um diameter. A buckling test of microneedle gave the result that there was no microneedle broken during the test via the guiding holes. Contrary, there were several microneedles broken during the penetration without the facilitation of the guide.

 
 
MICROPRESSURE SENSOR
 
 

The piezoresistive pressure sensor is reliable for precision pressure measurement. In our Lab., a silicon piezoresistive pressure sensor for high pressure measurement utilizing a combination of three-axis stress components has been developed. The piezoresistive pressure sensor can be used for measurement of internal pressure in a injection molding machine. The pressure sensor was composed of a force sensor, a stainless steel (SUS630) housing with a diaphragm of 10 mm-diameter in which the force sensor was assembled, a fix screw, a stainless steel (SUS630) case and a resin cap. Pressure is transmitted into force which is applied to four piezoresistors on a silicon sensor chip through a force transmission rod of glass (SW-3). Stresses due to applied pressure in piezoresistors depend on the diameter, height and Young's modulus of the rod, and the diaphragm thickness of the sensor chip. In order to obtain large resistance changes in piezoresistors, the optimum combination of three-axis stress components was investigated by changing of these parameters. An output of the prototyped pressure sensor was more than 50 mV / 5 V at 150 MPa and a sensitivity temperature characteristic was 0.11 % / centigrade in the range from room temperature to 150 centigrade.

 

  
 
SMART MEMS
  
 

 

  
  SENSOR NETWORK