Yasumasa Koda

Photodiode dopant structure with atomically flat Si surface for high-sensitivity and stability to UV light

In this work, n+pn-type photodiodes with various surface n+ layer profiles formed on the atomically flat Si surface were evaluated to investigate the relationships between the surface photo-generated carrier drift layer dopant profiles with a high uniformity and sensitivity and stability to UV-light. The degradation mechanism of photodiode sensitivitiy in UVlight wavelength due to UV-light exposure is explained by the changes in the fixed charges and the interface states at Si/SiO2 system above photodiode. Finally, a design strategy of photodiode dopant profile to achieve a high sensitivity and a high stability to UV-light is proposed.

A UV Si-photodiode with almost 100% internal Q.E. and high transmittance on-chip multilayer dielectric stack

In this work, by optimizing the structure and thickness of the on-chip multilayer dielectric stack using SiO2 and low extinction coefficient Si3N4 with the high UV-light sensitivity photodiode technology, high external Q.E. and high stability to UV-light were both successfully obtained. By changing the structure of on-chip multilayer dielectric stack and film thickness, we obtained the photodiode with the high external Q.E. in the desired UV-light region.

A wide dynamic range CMOS image sensor with 200–1100 nm spectral sensitivity and high robustness to UV right exposure

A highly UV-light sensitive and sensitivity robust CMOS image sensor with a wide dynamic range (DR) was developed and evaluated. The developed CMOS image sensor includes a lateral overflow integration capacitor in each pixel in order to achieve a high sensitivity and a wide DR simultaneously. As in-pixel photodiodes (PDs), buried pinned PDs were formed on flattened Si surface. The PD has a thin surface p+ layer with a steep dopant concentration profile to form an electric field that drifts photoelectrons to the pinned n layer. This structure improves UV-light sensitivity and its stability. In addition, a buried channel source follower driver was introduced to achieve a low pixel noise. This CMOS image sensor was fabricated by a 0.18-µm 1-polycrystalline silicon 3-metal CMOS process technology with buried pinned PD. The fabricated image sensor has a high sensitivity for 200–1100 nm light wave band, high robustness of sensitivity and dark current toward UV-light exposure and a wide DR of 97 dB. In this paper, the PD structures, the circuit, the operation sequence and the measurement results of this CMOS image sensor are discussed.

High quantum efficiency 200–1000 nm spectral response photodiodes with on-chip multiple high transmittance optical layers

High quantum efficiency (QE) 200-1000 nm spectral response photodiodes using on-chip multiple high transmittance optical layers are demonstrated for development of a high sensitivity linear photodiode array (PDA). In this paper, seven types of PDs with an optical layer each having a band-pass filter type transmittance are described. A surface photo-generated carrier drift layer is employed to improve internal QE and stability of sensitivity to UV-light. The average QE of 79% for 200-1000 nm and 84% for 200-380 nm were obtained for the fabricated PDs. In addition, after acceleration UV-light exposure, degradation of QE is below 15% and increment of dark current is less than double.

A 1024×1 linear photodiode array sensor with fast readout speed flexible pixel-level integration time and high stability to UV light exposure

In this paper, we demonstrate two types of new photodiode array (PDA) with fast readout speed and high stability to ultraviolet (UV) light exposure. One is a high full well capacity sensor specialized for absorption spectroscopy, the other one is a high sensitivity sensor for emission spectroscopy. By introducing multiple readout paths along the long side of the rectangle PD, both two PDAs have achieved more than 150 times faster readout speed compared with a general PDA structure with a single readout path along the short side of PD. By introducing a photodiode (PD) structure with a thin and steep dopant profile p+ layer formed on a flattened Si surface, a higher stability of the light sensitivity to UV light exposure was confirmed compared with a general PD structure for conventional PDAs.

An ultraviolet radiation sensor using differential spectral response of silicon photodiodes

An ultraviolet (UV) sensor is demonstrated with high sensitivity in the UV waveband and low sensitivity in the visible (VIS) and near-infrared (NIR) wavebands, utilizing only bulk silicon technology. The developed sensor utilizes the differential spectral response of photodiodes (PDs) with a high UV sensitivity (PD1) and a low UV sensitivity (PD2), for UV signal extraction under a VIS and NIR light background. To suppress the effects of incident light spatial strength distribution over the sensor, PD1 and PD2 were arranged in a checkered pattern of 8×6 PDs. High Signal to Noise Ratio (SNR) for UV signal extraction was achieved by a developed prototype UV sensor circuit consisted of charge amplifiers connected to PDs and a differential amplifier. The fabricated PD chip has a total area of 1.2 mm2, PD1 and PD2 showed a sensitivity of 0.16 A/W and 0.02 A/W at 310 nm, respectively. The spectral response of the UV sensor was measured and the UV waveband selective sensitivity was successfully obtained.