Sony’ Polarization Image Sensor Technology
Sony Semiconductor Solutions has launched a polarization image sensor (polarization sensor): 3.45µm pixel size with four-directional polarizer which is formed on the photodiode of the image sensor chip*1. This polarization sensor is targeting the industrial equipment market.
In addition to capturing brightness and color*2, this image sensor can also capture polarization information that cannot be detected by a normal image sensor. This polarization sensor can be used in many applications in the industrial field, such as inspection when visibility and sensing are difficult.
Polarsens is a CMOS Image Sensor pixel technology that has several different angle polarizer formed on chip during the semiconductor process allowing highly accurate alignment with pixel.
Source: Sony, IEDM2016, Lecture number 8.7
Sony Semiconductor Solutions’ polarization sensor can capture a four directional polarization image in one shot by the four directional polarizer (Fig.1). It can calculate the direction and degree of polarization (DoP) based on the intensity of each directional polarization. Together with subsequent signal processing, it can capture the polarization information*3 in real time*4.
With conventional types of polarization sensors, the polarizer is attached on top of the on-chip lens layer (Fig.2), however with Sony Semiconductor Solutions’ polarization sensor the polarizer is formed on chip under the on-chip lens layer (Fig.3). A shorter distance between the polarizer and the photodiode improves the extinction ratio*5 and the incident angle dependence.
Since the polarizer is formed during the semiconductor process, form and formulation of polarizer, uniformity, mass productivity and durability are excellent compared to conventional polarization sensors. Furthermore, Sony Semiconductor Solutions’ Polarization sensor is covered with an anti-reflection layer which helps to reduce reflectance and avoids poor flare and ghost characteristics.
Fig.2. Structure of Conventional Polarization sensor
Fig.3. Structure of Sony Semiconductor Solutions’ Polarization sensor
Industrial applications require imaging of fast-moving objects. However, existing CMOS image sensors are unable to accurately identify fast-moving objects, due to the focal plane distortion, which is caused by the rolling shutter function. The IMX250MZR/MYR, IMX253MZR/MYR address this issue by providing an analog memory inside each pixel and realizing the global shutter function to enable high-picture-quality without focal plane distortion.
The column-parallel A/D conversion technology of Sony CMOS image sensors is used to realize high-speed imaging of up to 163.4frame/s (ADC 8 bit) for the IMX250MZR/MYR, 68.3frame/s (ADC 8 bit) for the IMX253MZR/MYR. Increasing processing speed for industrial applications.
The IMX250MZR/MYR, IMX253MZR/MYR are equipped with variety of functions necessary for industrial applications, such as ROI Mode and Trigger Mode. ROI Mode crops required areas, and up to 8 × 8 = 64 locations can be set with IMX250MZR/MYR. In addition to setting the 8 × 8 = 64 locations, IMX250MZR/MYR provides greater freedom for specifying regions and allows overlap of specified regions. Various exposure methods are provided for trigger mode, which controls the exposure time using an external pulse.
Light has physical elements : brightness (amplitude), color (wavelength) and polarization (vibration direction). Lights from the Sun or fluorescent lamps vibrate in various directions and is called unpolarized light.
Sony Semiconductor Solutions’ polarization sensor has wire-grid polarizers. Parallel light against polarizer passes through it, while perpendicular light is cut off at the polarizer.
Polarization has two physical information, which are the degree of polarization and the direction of polarization. This information can be used for various applications such as surface scratch detection, particle inspection, distortion and shape recognition which has traditional been difficult to detect.
The light is reflected by the surface of the object in polarized and unpolarized lights. The DoP of the reflected light depends on the surface condition (material, color, roughness etc.) and the angle of reflection.
Fig.5. Normal image
Fig.6. Degree of Polarization image
In the Degree of Polarization image (Fig.6) the white is high polarization and black is low polarization.
As example, the stitch is easily visible due to the difference in the degree of polarization of the thread and leather.
Polarization direction provides the direction information of reflected plane of an object.
Fig.7. Normal image
Fig.8. Polarization Direction image
The direction of polarization image (Fig.8) shows the angle of the polarization direction in color using HSV color mapping (Fig.9).
In this example, the upper side of the cube is highlighted in light blue meaning that the angle of the polarization direction is 90 degree (according to Fig.9).
Fig.9. HSV color mapping
Fig.10. Normal image
Fig.11. Degree of Polarization image
These examples show dents and dust on a homogenous glass plane. We can easily find scratches and stains (fingerprint and dust) due to differences in the degree of polarization. (Fig.10,11)
Fig.12. Normal image
Fig.13. Degree of Polarization image
Thanks to the difference in the degree of polarization between the tablet and the aluminum package, it is easy to identify whether the tablets are filled in or not. (Fig.13)
Fig.14. Normal image
Fig.15. Polarization Direction image
With the information of direction of polarization, we can identify both distortions and the direction of distortion of the plane. (Fig.15)
Fig.16. Normal image
Fig.17. Removed reflection image
Polarization information can be used to remove reflections (Fig.17). Sony Semiconductor Solutions’ polarization sensor has a four-directional polarizer, which can simultaneously remove the reflections in multi planes.(Fig.17)
All images were generated by Sony Semiconductor Solutions’ polarization sensor ’s evaluation board.
Diagonal 11.1 mm (Type 2/3) Approx. 5.07M-Effective Pixel Monochrome/Color Polarization CMOS Image Sensor
Diagonal 17.6 mm (Type 1.1) Approx. 12.37M-Effective Pixel Monochrome/Color Polarization CMOS Image Sensor
IMX250MZR / MYR
|Image size||Progressive scan mode : Diagonal 11.1 mm (Type 2/3)
Full-HD mode : Diagonal 7.7 mm (Type 1/2.35)
|Progressive scan mode : Diagonal 17.6 mm (Type 1.1)|
|Number of effective pixels||2464 (H) × 2056 (V)
Approx. 5.07 M pixels
|4112 (H) × 3008 (V)
Approx. 12.37 M pixels
|Unit cell size||3.45 µm (H) × 3.45 µm (V)|
|Optical blacks||Horizontal||Front: 0 pixels, rear: 0 pixels|
|Vertical||Front: 10 pixels, rear: 0 pixels|
|Input drive frequency||37.125 MHz / 54.0 MHz / 74.25 MHz|
|Supply voltage VDD (Typ.)||3.3 V / 1.8 V / 1.2 V|
|Sensitivity (monochrome)||Typ.[F8]||342 mV||TBD||3200 K, 706 cd/m2、
|Saturation signal||Min.||1001 mV||TBD||Tj = 60 °C|
|Product name||Drive mode||Recommended number of recording pixels||ADC
|Frame rate (Max.)
|IMX250MZR/MYR||Progressive scan||2448 (H) × 2048 (V)
Approx. 5.01 M pixels
|Full-HD||1920 (H) × 1080 (V)
Approx. 2.07 M pixels
|IMX253MZR/MYR||Progressive scan||4096 (H) × 3000 (V)
Approx. 12.29 M pixels
Subject to test and environment conditions* IMX253MZR (TBD)
IMX250MZR/MYR are the Sony's first and world's smallest*6 pixel size (IMX250MZR/MYR) and the world's first*6 color (IMX250MYR) polarization image sensor thus far as the commercially available product. By creating a unique air gap structure in the polarizer, it enables excellent polarization properties and sensitivity in a broad band from visible to near infrared. It also has an advantage of excellent image quality in various light source environments by introducing the world's first*6 anti-reflection layer to reduce flare and ghost for polarization sensor.
In order to achieve the required polarization properties and sensitivity, it is necessary to control the each wire grid's shape very precisely in units of nanometers. When I realized the fact by simulation, I was worried if it could actually be manufactured. And we did not know whether a unique air gap structure can be created without manufacturing and quality assurance issues. When launching the polarization evaluation environment, the definitions of the words were different from each other, like the origins of the polarization angle, the direction of rotation, whether polarized light is represented by electric field or magnetic field, and so on. I am very glad to know that cleared all these tasks, confirmed the required properties, and now ready to ship. I especially appreciate the factory members which managed to realize the idea which was initially thought impossible.
Mr. Yamagishi Mr. Nishide Mr. Maruyama
From left in the back row:
Mr. Terada Mr. Hayashi Mr. Fukushima
From left in the front row:
Mr. Yamazaki Mr. Matsuno