Tzu-an Hsu

Light guide for pixel crosstalk improvement in deep submicron CMOS image sensor

Light guide, a novel dielectric structure consisting of PE-Oxide and FSG-Oxide, has been developed to reduce crosstalk in 0.18-/spl mu/m CMOS image sensor technology. Due to the difference in refraction index (1.46 for PE-Oxide and 1.435 for FSG-Oxide), major part of the incident light can be totally reflected at the interface of PE-Oxide/FSG-Oxide, as the incidence angle is larger than total reflection angle. With this light guide, the pixel sensing capability can be enhanced and to reduce pixel crosstalk. Small pixels with pitch 3.0-/spl mu/m and 4.0-/spl mu/m have been characterized and examined. In 3.0-/spl mu/m pixel, optical crosstalk achieves 30% reduction for incidence angle of light at 10/spl deg/.

Air-gap guard ring for pixel sensitivity and crosstalk improvement in deep sub-micron CMOS image sensor

An air-gap guard ring around the pixel sensor, to improve pixel sensitivity and crosstalk, in 0.18 /spl mu/m CMOS image sensor technology has been successfully developed. By using the RI (refractive index) difference between the air gap (RI/spl sim/1) and dielectric films (RI=1.4/spl sim/1.6), the major incident light is collected in the targeted pixel due to the total internal reflection occurred in the air-gap/dielectric-film interface. The small pixel pitch of 2.8 /spl mu/m/spl sim/4.0 /spl mu/m has been characterized and demonstrates excellent optical performance. For a 3.0 /spl mu/m pixel, the pixel sensitivity shows 45% enhancement and optical spatial crosstalk achieves 90% reduction at 20/spl deg/ incident angle.

Dramatic reduction of optical crosstalk in deep-submicrometer CMOS imager with air gap guard ring

A dielectric structure, air gap guard ring, has been successfully developed to reduce optical crosstalk thus improving pixel sensitivity of CMOS image sensor with 0.18-/spl mu/m technology. Based on refraction index (RI) differences between dielectric films (RI = 1.4 /spl sim/ 1.6) and air gap (RI = 1), total internal reflection occurred at dielectric-film/air-gap interface, thus the incident light is concentrated in selected pixel. Excellent optical performances have been demonstrated in 3.0 /spl times/ 3.0 /spl mu/m pixel. Optical spatial crosstalk achieves 80% reduction at 20/spl deg/ incidence angle and significantly alleviates the pixel sensitivity degradation with larger angle of incident light.

Color mixing improvement of CMOS image sensor with air-gap-guard ring in deep-submicrometer CMOS technology

In this letter, color mixings of a CMOS image sensor with air-gap-guard-ring (AGGR) and conventional structures were investigated in 0.18-/spl mu/m CMOS image sensor technology. As the light incident angle is increased from 0/spl deg/ to 15/spl deg/, conventional pixel shows serious color mixing. For example, the maximum photo responses of blue, green1, green2, and red pixels are shifted from 490 to 520 nm, 530 to 500 nm, 530 to 600 nm, and 600 to 580 nm, respectively. However, pixels with AGGR not only keep correct spectral response without peak shift but also achieve 5%-50% crosstalk reduction, thus preventing the sensor from color mixing efficiently.

A high-efficiency CMOS image sensor with air gap in situ MicroLens (AGML) fabricated by 0.18-/spl mu/m CMOS technology

The air gap in situ microlens (AGML) above-pixel sensor with 0.18-/spl mu/m CMOS image sensor technology has been successfully developed to dramatically improve the optical crosstalk and pixel sensitivity. We demonstrated excellent crosstalk diminution with the structure on small pixels. Compared with conventional 2.8 /spl mu/m square pixel, adopting the AGML can reduce the optical crosstalk up to 64%, and provide 21% in enhancement of photosensitivity at 0/spl deg/ incident angle. Furthermore, under 20/spl deg/ incident angle the optical crosstalk reduction and sensitivity enhancement are increased to 89% and 122%, respectively. Therefore, the AGML structure makes pixel size be further scaled down to less than 2.8 /spl mu/m square and maintain good performance.

An effective method to improve the sensitivity of deep submicrometer CMOS image sensors

An effective method has been successfully developed to improve the sensitivity of deep sub-micrometer CMOS image sensors (CIS). In advanced CIS technology, the shallow trench isolation (STI) SiO/sub 2/ on the photodiode and the SiON film are used for silicide blocking and as a contact etching-stop layer, respectively. However, the dielectric structure, which is composed of an interlayer dielectric/SiON/STI/spl I.bar/SiO/sub 2//Si, causes a destructive interference and thus degrades quantum efficiency (QE), especially at short wavelengths. In this paper, an effective method for improving CIS sensitivity has been proposed, based on both theoretical analysis and simulation results, by removing the STI from the photodiode area and then forming a deposition of SiON. Experimental results show that a 40% QE improvement can be achieved under the irradiance of light at a wavelength of 450 nm.

The mechanism and evaluation of hot-carrier-induced performance degradation in 0.18-/spl mu/m CMOS image sensor

An effective method to evaluate the hot-carrier-induced pixel performance degradation of 0.18-/spl mu/m CMOS active pixel sensor has been reported. The hot carriers generated at the source follower transistor and absorbed by the nearby photodiode will cause the pixel performance degradation such as increase of dark signal and decrease of operation range. Based on the detailed measurements through overall operation conditions, a simple method has been proposed to evaluate the degradation induced by the hot carriers and, thus, provides a design guide to predict pixel performance.