Takeshi Hizawa

32 × 32 pH Image Sensors for Real Time Observation of Biochemical Phenomena

32 x 32 pH image sensors were successfully fabricated by using the CCD/CMOS image sensor technique, and real time imaging of a chemical reaction and pH distribution was carried out for the first time. The pH variations by a chemical reaction are observed by 200 ms step (i.e. 5 flames per sec). The pH image sensor was able to take a pH image of mouse stomach successfully. It means that the novel image sensor can be applied to a biomedical and biochemical field.

Charge Transfer Type pH Sensor with Super High Sensitivity

We successfully fabricated a super high sensitivity charge transfer type pH sensor. The proposed pH sensor is possible to amplify the sensing signals without an external amplifier by accumulation cycle. The pH sensitivity was obtained 5048 mV/pH, which is approximately 100 times higher than the Ion Sensitive Field Effect Transistor (ISFET), which is the most familiar pH sensor using semiconductor. This is the highest sensitivity of pH in the past. The performance of this charge transfer type pH sensor is equal with glass electrode type pH sensor. In addition, the charge transfer type pH sensor has much possibility to exceed the glass electrode method.

Sensing Characteristics of Charge Transfer Type pH Sensor by Accumulative Operation

We present about a pH sensor, which is capable of measuring high sensitivity using charge transfer technique. The sensitivity of pH was obtained 1130 mV/pH by charge accumulation operation. The proposed pH sensor using charge transfer technique is possible to increase a sensing signal without an extra amplifier. It is expected that charge transfer type pH sensor increases sensitivity and decreases random noise.

Characteristics of highly sensitive ph sensors with charge accumulation operation

A charge-transfer-type pH sensor operated by charge accumulation was demonstrated, and it was confirmed that its pH sensitivity was 1130 mV/pH with five signal integration cycles. The most familiar pH sensor using a semiconductor is the ion-sensitive field effect transistor (ISFET). The sensitivity of our pH sensor was 20 times higher than that of the ISFET. The sensitivity of the ISFET, which is similar in structure to a metal–insulator–semiconductor (MIS) structure, is restricted by the Nernst equation (59 mV/pH at room temperature). The output signal from an ISFET disappears into its noise as pH variation becomes small. The charge-transfer-type pH sensor increases the pH output signal to integrate signals in the time domain that are noise-free. It is expected that with this sensor it is possible to measure small pH signal variations.

Novel fused sensor for photo and ion sensing

A novel sensor array, which is fused photo-sensors and ion sensors, is proposed and the prototype one was successively fabricated using a CMOS process. On the proposed sensor, a photo sensor and an ion sensor are fused in a same pixel, and photo-signal and ion concentration density are detected in a same sensing area and a same time. Therefore, relationship between light distribution and ion distribution will be clear by using this novel sensor array. The input light power dependences of the photo sensing part were measured, and it can be found that the output signals are proportional to the input light power and there is no influence of the pH value in solutions. The dependences on pH signal were also investigated. It is also found that there is no influence of the light intensity.

Filter-less fluorescence sensor with high separation ability achieved by the suppression of forward-scattered light in silicon

The improvement of a filter-less fluorescence sensor, by suppressing forward scattering in silicon by surface planarization is presented. A fluorescence microscope has been widely used in biochemical fields. However, it is difficult to miniaturize because optical filters and other parts are necessary. We previously developed a filter-less fluorescence sensor. The separation ability of excitation light and fluorescence in the previous device was 550:1. It is necessary to improve the separation ability. This study focuses on the suppression of forward-scattered incident light in silicon, through the enhanced surface planarization of polysilicon, which is the gate electrode material. The separation ability of the filter-less fluorescence sensor was increased from 550:1 to 1250:1 by the suppression of forward-scattered light.

Fabrication of 2D pH CMOS image sensors and real time imaging of chemical reaction

We present about pH image sensors, which are capable of measuring 2D distribution of various chemical reaction in real time. The pH CMOS image sensor using charge transfer technique is a novel pH sensor and imaging sensor that is capable of measuring variations on the chemical reaction as an image, and it was fabricated by CMOS (complimentary metal-oxide semiconductor) circuit process technology. Prototype pH CMOS image sensors are successfully fabricated and measured 2D distribution of various chemical reactions in moving image at 1/30 sec per 1 frame. It is expected that the pH CMOS image sensor is able to use for novel applications such as medical and biochemistry field.

Optical-Interferometry-Based CMOS-MEMS Sensor Transduced by Stress-Induced Nanomechanical Deflection

We developed a Fabry–Perot interferometer sensor with a metal-oxide-semiconductor field-effect transistor (MOSFET) circuit for chemical sensing. The novel signal transducing technique was performed in three steps: mechanical deflection, transmittance change, and photocurrent change. A small readout photocurrent was processed by an integrated source follower circuit. The movable film of the sensor was a 350-nm-thick polychloro-para-xylylene membrane with a diameter of 100 µm and an air gap of 300 nm. The linearity of the integrated source follower circuit was obtained. We demonstrated a gas response using 80-ppm ethanol detected by small membrane deformation of 50 nm, which resulted in an output-voltage change with the proposed high-efficiency transduction.

Improvements of low-detection-limit filter-free fluorescence sensor developed by charge accumulation operation

We developed a low-detection-limit filter-free fluorescence sensor by a charge accumulation technique. For charge accumulation, a floating diffusion amplifier (FDA), which included a floating diffusion capacitor, a transfer gate, and a source follower circuit, was used. To integrate CMOS circuits with the filter-free fluorescence sensor, we adopted a triple-well process to isolate transistors from the sensor on a single chip. We detected 0.1 nW fluorescence under the illumination of excitation light by 1.5 ms accumulation, which was one order of magnitude greater than that of a previous current detection sensor.

Fabry-perot interferometric surface-stress sensor with high wavelength selectivity for label-free biosensing

We developed a MEMS Fabry-Perot interferometer with high wavelength selectivity by using Au half-mirrors for a highly sensitive label-free biosensor. The proposed optical interferometer can perform signal conversion from membrane deformation caused by biomolecule adsorption to electrical readout signal in an exponential manner by using the gradient of the transmitted interference spectrum. By integrating 50-nm-thick Au half-mirrors, wavelength selectivity improved to be 6.5 times. We successfully demonstrated spectral shift of 40 nm caused by membrane deflection due to BSA antigen-antibody reaction on the optical interferometric sensor.