Development of Micro Solar Boat Employing Ion Drag Force

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As the power source for a Micro Solar Boat (MSB) to be developed, we have fabricated a new micro solar cell, which consists of four cells made of GaAs connected in series. The size of the micro solar cell is about 700mum*900mum. The open-circuit voltage of 3.8 V was obtained, and the short-circuit current amounted to 19muA when it was illuminated by a laser beam of 2.3 mW.Since the required voltage for a driving electrodes of 20mum spacing is 3 V,the above characteristics of the micro solar cell is enough to be used in the MSB.In a seriesly-connected solar cell module, a short-circuited cell would decrease the total output voltage. To avoid this, the yield of the micro solar cells on a wafer should be high. Inspection by electron beam induced current (EBIC) images was usefully employed in evaluating the solar cells.On the other hand, as the driving mechanism for the MSB,a pair of interdigital electrodes has been designed to facilitate a uniform flow of fluid, while a barrier layr that … More prevent charge exchange of ions was redesigned to protect most of the electrode, which results in less erosion of the metal electrode. With these considerations micro interdigital electrodes were fabricated on wafer, and fluid flow characteristics as well as current-voltage characteristics were examinedimmersed in liquid. The experiment showed, for example, that application of 3 V resulted in the fluid flow velocity of the order of 1 cm/s and the current of 0.1muA in the liquid of butyl alcohol.In combining the two elements in an MSB,a whole structure was designed into 0.8mm*1.2mm, and process techiniques needed to complete it were developed : a via-hole techniqued to connect the interdigital electrodes on the rear surface to the micro solar cell on the front surface, and a technique to form electrodes and lead lines on undulated wafers. The completed MSBs were tested floated on water under the light beam of a high-power diode laser. The motion was recorded by a video recorder and then analyzed. Continual straight movements in an expected direction was observed for four minutes, and the average velocity was 0.1mm/s. Thus we have succeeded in developing a novel micromachine named Micro Solar Boat, which employs an ion drag effect as its driving force.In addition, the same driving principle was applied to a rotary microactuator, where electrohydrodynamic flow by the iron drag force rotated a rotor of 4mm across. A DC motor that has a spped of 3000rpm has been successfully fabricated. Less