Deep Trench Isolation and Inverted Pyramid Array Structures Used to Enhance Optical Efficiency of Photodiode in CMOS Image Sensor via Simulations

Abstract

The photodiode in the backside-illuminated CMOS sensor is modeled to analyze the optical performances in a range of wavelengths (300–1100 nm). The effects of changing in the deep trench isolation depth (DTI) and pitch size (d) of the inverted pyramid array (IPA) on the peak value (OEmax.) of optical efficiency (OE) and its wavelength region are identified first. Then, the growth ratio (GR) is defined for the OE change in these wavelength ranges to highlight the effectiveness of various DTI and d combinations on the OEs and evaluate the OE difference between the pixel arrays with and without the DTI + IPA structures. Increasing DTI can bring in monotonous OEmax. increases in the entire wavelength region. For a fixed DTI, the maximum OEmax. is formed as the flat plane (d = 0 nm) is chosen for the top surface of Si photodiode in the RGB pixels operating at the visible light wavelengths; whereas different nonzero value is needed to obtain the maximum OEmax. for the RGB pixels operating in the near-infrared (NIR) region. The optimum choice in d for each color pixel and DTI depth can elevate the maximum GR value in the NIR region up to 82.2%.

Single microhole per pixel for thin Ge-on-Si complementary metal-oxide semiconductor image sensor with enhanced sensitivity up to 1700 nm

“…In the 3D simulation setup, the transmittance associated with 900 nm thickness is used for the pigment filters, 1 , 21 – 23 and the parameters are listed in Table 1. The filter’s response spectrum was calculated from the refractive index presented in Table 1.…”

“…Silicon photonics has gained attention due to an increased demand for complementary metal-oxide semiconductor (CMOS) compatible near-infrared (NIR) image sensors 1 – 5 for mobile imaging, digital cameras, surveillance, remote monitoring, and biometrics as against the conventional III-V-based sensors. Several approaches are reported to increase pixel density.…”

Development of 4-μm-pixel Pitch NIR Multispectral Imaging Sensor and Its Application to Glare-free NIR Color Fundus Camera

“…We selected the standard type because the IR-enhanced type is more likely to cause cross-talk between pixels owing to an IPA surface in narrow pixel pitches, resulting in inaccurate wavelength resolution. (12,13) This is particularly concerning because NIR light penetrates deep into silicon and generates photocarriers reaching the neighboring pixels, (14) whereas the selected sensor does not have mechanical solutions preventing cross-talk, for example, deep trenches between the pixels. Although a standard sensor may not exhibit the same level of IR sensitivity as an IR-enhanced sensor, particularly beyond 900 nm, we have prioritized wavelength resolution to attain the IR multispectral advantage.…”

Design of a CMOS image sensor pixel with embedded polysilicon nano-grating for near-infrared imaging enhancement

“…Therefore, some studies have investigated a detector 30 with a thicker active layer in silicon [14,15], making the photo-31 sensitive layer going deeper in the silicon with high resistivity 32 epitaxial layer [16,17] or by applying a negative voltage at the 33 back of the photodiode [12] . Unfortunately, these solutions re- extensively studied [18][19][20][21]. In addition, the principle of high ab-42 sorption by a structure combining plasmonic diffraction and the 43 use of metallic trenches has been demonstrated [22].…”