Sony Semiconductor advances its SWIR imaging technology for industrial applications
Sony Semiconductor Solutions (SSS) has announced the release of IMX992 and IMX993 short-wavelength infrared image sensors, specifically designed for industrial applications. According to the company, both of these imaging sensors have small pixel sizes, enabling a more compact sensor design without compromising on resolution. However, the challenge with smaller pixels is that they tend to collect less light, which can be a disadvantage in low-light scenarios. Sony has optimized the pixel structure to efficiently capture light and mitigate this potential drawback.
Sony’s SWIR sensors have the ability to capture images across a wide spectrum, a crucial feature for industrial applications. In industries like semiconductor wafer bonding and defect inspection, SWIR imaging can reveal subsurface anomalies and bonding issues that are otherwise invisible in the regular light spectrum. Similarly, in the food production sector, these sensors can detect contaminants and inspect ingredients.
“Sony Semiconductor Solutions created high-quality compound semiconductor photodiodes at its own manufacturing facilities and optimized the readout circuits for the SWIR image sensor using its accumulated circuit technology. By connecting these circuits with Cu-Cu bonding, SSS has achieved a unique SWIR image sensor,” says Natsuko Mizumachi, corporate strategy department at Sony Semiconductor Solutions Corporation.
The new sensors have the capacity to deliver high-resolution images, even with their small pixel size. This is important for identifying defects or details within industrial processes. Furthermore, their enhanced performance in low-light conditions means that they can function effectively in environments where lighting may not be optimal, particularly in challenging edge locations. These capabilities of SWIR sensors open up new possibilities in industrial imaging, according to the company’s statement.
Sony has tackled the challenge of reducing noise in low-light conditions by introducing new shooting modes (HCG and LCG) that enhance low-light imaging. For low light imaging capabilities, Sony uses the high conversion gain mode (HCG) in its SWIR sensor. This mode operates by amplifying the signal immediately after it is converted from light to an electrical signal, effectively minimizing the introduction of noise. In contrast, the low conversion gain model is optimized for bright environments.
“In dark environments with limited light, HCG mode directly amplifies the signal with minimal noise after being converted to an electrical signal from light, thereby relatively reducing the amount of noise downstream,” Mizumachi explains.
To achieve a high pixel count within a compact pixel size, Sony employs a Copper-Copper (Cu-Cu) bonding technique between the InGaAs (Indium Gallium Arsenide) layer and the Silicon layer. The InGaAs layer forms the essential photodiode of the light-receiving unit, responsible for capturing infrared light and converting it into electrical signals. Meanwhile, the Silicon layer constitutes the readout circuit, which processes these electrical signals into digital data. Sony’s proprietary Cu-Cu bonding methods streamline the integration of these layers.
“The pixel chip and the logic circuit chip in stacked CMOS image sensors are directly connected via copper (Cu) terminals formed on each layered surface. This eliminates the need for a dedicated area to pass through and connect both chips, making it possible to reduce the size of the image sensor,” Mizumachi explains.
In an exclusive interview with EdgeIR, Mizumachi discussed how they are addressing a significant challenge in the development of an industrial CMOS image sensor. They emphasized the importance of maintaining a certain bump pitch in the context of an image sensor, as it is important for effective bonding.
However, a limitation arises when there is a minimum feasible bump pitch, which in turn restricts the potential reduction in pixel size. This limitation stems from the need to connect each pixel, and if the pixels are placed too closely together, the bumps cannot be accommodated without overlapping.
To overcome this challenge, Mizumachi explained, “With SSS’s technology, our Cu-Cu connection enables a finer pixel pitch and smaller pixels. As a result, smaller high-resolution cameras can be developed, which can support higher inspection precision.”
Regarding future plans for SWIR sensor development, when asked, Sony refrained from disclosing specific details about their roadmap. However, they acknowledged that one potential direction for development is to enhance resolution. The company expressed its intent to evaluate customer feedback on the upcoming IMX992 and IMX993, scheduled for release in February 2024, as part of its strategic considerations.
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