Masahiro Mitani

Multimodal Complementary Metal–Oxide–Semiconductor Sensor Device for Imaging of Fluorescence and Electrical Potential in Deep Brain of Mouse

We have developed a multimodal complementary metal–oxide–semiconductor (CMOS) sensor device for observing neural activities in the deep brain of a mouse. The CMOS sensor includes an image sensor, electrodes, and a light-emitting diode (LED). The image sensor was designed to be operated using only four inputs/outputs (I/Os) to reduce the number of connecting wires. The electrodes were placed on the pixel array of the sensor. Windows were opened in the electrode over the photodiodes to enable the fluorescence to be imaged using the pixels under the electrodes. An LED was mounted on the chip. The sensor chip was shaped like a shank to facilitate smooth insertion into the brain tissue. The entire device was coated with a parylene layer to make it biocompatible. The experimental results showed that the green fluorescent beads on the pixel array were successfully imaged using the LED on the chip as a light source. In a brain phantom, the change in the electrical potential was successfully sensed by the electrode, and green fluorescent beads were simultaneously imaged using the pixels under the electrode. We also demonstrated that the CMOS sensor device could successfully operate in the hippocampal area of an anesthetized mouse.

Implantable Image Sensor with Light Guide Array Plate for Bioimaging

We propose and demonstrate the fabrication of a light guide array (LGA) structure to improve the spatial resolution of an implantable image sensor. An LGA structure is composed of an array of holes with a high aspect ratio. By restricting the incident angle into image sensor pixels, unwanted incident light is eliminated and degradation of the spatial resolution owing to the gap from the image sensor is reduced. An LGA plate is fabricated by etching holes on a silicon wafer. The LGA plate is embedded on an image sensor and the improvement of spatial resolution is verified. As an example, images of fluorescent beads were obtained using the image sensor with the LGA plate. The imaging contrast and resolution were successfully enhanced.

Ultrahigh-Performance Polycrystalline Silicon Thin-Film Transistors on Excimer-Laser-Processed Pseudo-Single-Crystal Films

Thin-film transistors (TFTs) were fabricated on polycrystalline silicon (poly-Si) films formed by position-controlled large-grain growth technology using an excimer laser. The field-effect mobility, on-off transition slope, and threshold voltage were 914 cm2 V-1 s-1, 93 mV/decade, and 0.58 V for the n-channel device, and 254 cm2 V-1 s-1, 122 mV/decade, and -0.43 V for the p-channel device, respectively. These values indicate that TFTs had an ultrahigh performance comparable to that of {100}-oriented crystal-silicon metal–oxide–semiconductor (MOS) transistors. Furthermore, their effective mobilities had the same effective field and temperature dependences as those of MOS transistors, indicating that electrons and holes were predominantly scattered not by random grain boundaries or defects in the Si film, but by phonons at the SiO2–Si interface, similarly to those of crystal-silicon MOS transistors. These attractive results were obtained as a result of the fact that the TFT channel region was made up of nearly {100}-oriented single grains.

Complementary Metal Oxide Semiconductor Based Multimodal Sensor for In vivo Brain Function Imaging with a Function for Simultaneous Cell Stimulation

We have developed a multimodal complementary metal oxide semiconductor (CMOS) sensor device embedded with Au electrodes for fluorescent imaging and cell stimulation in the deep brain of mice. The Au electrodes were placed on the pixel array of the image sensor. Windows over the photodiodes were opened in the electrode area for simultaneous fluorescent imaging and cell stimulation in the same area of the brain tissue. The sensor chip was shaped like a shank and was packaged by two packaging methods for high strength or minimal invasion. The experimental results showed that the 90 ×90 µm2 Au electrodes with windows were capable of injecting theta burst stimulation (TBS)-like current pulses at 0.2–1 mA in a saline solution. We successfully demonstrated that fluorescent imaging and TBS-like current injection can be simultaneously performed in the electrode area of a brain phantom.

P-194L: Late-News Poster: High-Frequency Performance of Sub-Micrometer Channel-Length Si TFTs Fabricated on Large Grain Poly-Si Films

High-frequency characteristics of sub-micron Si TFTs fabricated on large-grain poly-Si films are demonstrated for the first time. A cutoff frequency (fT) of 6 GHz and a maximum oscillation frequency (f max) of 25 GHz were obtained for the TFT with a channel length of 0.5 μm. It was confirmed that use of insulating substrates is advantageous to reduce the parasitic susceptance due to a conductive substrate, thereby increasing f max.

Relationship between Thin-Film Transistor Characteristics and Crystallographic Orientation in Excimer-Laser-Processed Pseudo-Single-Crystal-Silicon Films

The characteristics of thin-film transistors (TFTs) fabricated on pseudo-single-crystal (PSX)-Si thin films were examined. The variations of mobility were more than the theoretical values derived from the crystallographic orientation dependence of a bulk Si metal–oxide–semiconductor (MOS) transistor. To clarify the origin of this discrepancy, the relationships between the TFT characteristics and the crystallographic orientation of Si films in the channel region were investigated by using an electron backscattering pattern (EBSP) method. It was found that the surface orientation dependence for the PSX-Si TFT was different from that for a bulk Si MOS transistor, especially for the p-channel mode. A group of TFTs having a nearly {100}-oriented nucleus had a mobility close to those of simultaneously processed silicon-on-insulator (SOI) devices in the p-channel mode as well as in the n-channel mode. In contrast, a group of TFTs having a nearly {110}-oriented nucleus had a low and widely scattered mobility. The reason for these results is that twin boundaries with dislocations are easily generated in a grain grown from a {110}-oriented nucleus in order to compensate for the difference of the growth rates in different directions.

Partial Recovery of Photodegradation at Room Temperature in Hydrogenated Amorphous Silicon

Detailed ESR measurements disclosed that neutral Si dangling bonds (DBs) created by light soaking (LS) disappear partially at room temperature in a few hours after LS. In contrast metastable DBs created by thermal quenching remain unchanged at room temperature. It is suggested that a part of the Si DBs created by LS have a small activation energy for thermal annealing.

A CMOS sensor for in-vivo fluorescence and electrical imaging in a mouse brain

We report a complementary-metal-oxide-semiconductor (CMOS) image sensor for in-vivo imaging. The sensor is implemented on a flexible substrate with LEDs as excitation light sources. The images are successfully obtained in a mouse brain. We demonstrate a image contrast improvement method on the basis of image processing and multiple readout in order to overcome non uniform illumination of the excitation light.

A Multimodal CMOS Sensor Device with an On-Chip Mounted LED and Electrodes for Imaging of Fluorescence and Electrical Potential in a Mouse Deep Brain

Graduate School of Materials Science, Graduate School of Biological Sciences, Nara Institute of Science and Technology JST, CREST 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan, Phone: +81-743-72-6051, E-mail: ohta@ms.naist.jp