Superior low light photography

In low light photography flash is typically used to illuminate objects and persons that are situated close enough to the camera. The problem is, however, that the flash has only very little effect on objects, persons, or background that are situated further away from the camera. Consequently, in a typical low light flash photograph a person is brightly illuminated while the background remains pitch black. Another issue is that the use of a standard camera / phone mounted direct flash results in unnaturally appearing images.

In order to improve the low light image quality it would be necessary to collect enough light from objects, persons, or background that are situated further away from the camera necessitating the use of a long exposure time. This applies naturally also to objects and persons situated in the proximity of the camera in case the use of flash is completely omitted. The problem with long exposure time images is, however, that image blur is easily resulted in due to the movements of the camera and persons.

The only way to avoid the formation of image blur is to readout the camera with a fast enough frame rate and to compose the long exposure time image by merging frames together. In present CCD and CMOS image sensors the problem is that the frame merging increases the noise considerably. The benefit of Pixpolar’s Modified Internal Gate (MIG) image sensor technology is that the frame merging does not increase the noise. This means that the MIG sensors require a far shorter exposure time in low light than present image sensors in order to reach similar image quality. For example, depending on the circumstances, the exposure time can be more than halved with MIG sensors.

When similar exposure time is used in low light the image quality will be considerably better in MIG sensors when compared to traditional sensors. In dark image areas much more detail will be seen with the MIG image sensor than with traditional image sensors which improves significantly the dynamic range in the low end of the dynamic range scale. For further information on Pixpolar’s advantages on low light photography please refer to this white paper.

Another benefit of MIG sensors is that they do not suffer from interface issues like traditional CCD and CMOS image sensor technologies enabling the substrate material in MIG sensors to be changed from Silicon (Si) to Gallium Arsenide (GaAs). The advantage of GaAs is that it enables much smaller noise than silicon (larger band-gap of GaAs provides much lower dark current than silicon).

 

No more presetting of ISO in DSLRs

A great benefit of the MIG sensors is that the signal can be read-out accurately multiple times (due to Non-Destructive Correlated Double Sampling, NDCDS, ability). This means that one can provide the same image with multiple different ISO values. Thus one can either choose afterwards the best ISO setting or one can use different ISO values in different parts of the image. In the latter case the ISO value in each pixel is chosen e.g. such that the ISO is increased until the exposure value of the pixel exceeds a certain limit. This has also the unforeseen advantage that the amount of bits required in the Analog to Digital Converter (ADC) can be reduced while at the same time the Dynamic Range (DR) of the image can be improved.

If rolling shutter is utilized, which is typically the case in digital cameras, the reading of the signal multiple times with different ISO values bears the disadvantage that more skew is resulted in. However, in Digital Single Lens Reflex (DSLR) cameras mechanical shutter is typically used which means that the images are free of skew. Thus the MIG sensors offer for the DLSRs (and generally for digital cameras equipped with a mechanical shutter) a unique ability to afterwards adjust the ISO settings.

 

Security & Surveillance: unprecedented identification capability

Pixpolar’s MIG image sensor technology enables unprecedented identification capability due to low cross-talk and high Quantum Efficiency (QE) for Near Infra-Red (NIR) light as well as due to the fact that MIG sensor cannot be distracted with bright light sources. For further information please refer to Pixpolar’s leaflet on Security & Surveillance.

 

Night vision: unprecedented low light performance

The problem with traditional CCD and CMOS image sensor technologies is that they suffer from interface issues which severely limit their performance and usability in other semiconductor materials than silicon. The MIG image sensors do not suffer from interface issues and consequently Silicon Germanium (SiGe) and Germanium (Ge) based MIG sensors enable superior low light performance when compared to traditional image sensors or image intensifier tubes. An additional benefit of MIG sensors is that they are durable, cannot be distracted or damaged with bright light sources, and have very low cross-talk unlike image intensifier tubes.

With the help of Pixpolar’s MIG technology the safety of cars, planes, and boats can be improved considerably. Ultimately, germanium based MIG image sensors will offer humans unprecedented ability to see in the dark.

 

Ultimate thermal imaging performance

The performance of (e.g. HgCdTe based) thermal imagers can be greatly improved since MIG sensors do not suffer from interface issues. This fact provides the truly life saving ability to improve the probability of finding lost people in search and rescue missions.

 

Superior fire and spark detectors

The fact that the MIG sensors do not suffer from interface issues enables silicon carbide based superior solar-blind UV sensors for fire and spark detections. This fact facilitates early detection of fires improving the fire security and reducing the number of fire casualties for example due to forest fires. The economic and ecological losses due to fires will be also diminished.

 

Space Applications

The MIG image sensors are extraordinary tolerant to radiation since they do not suffer from interface issues. Consequently, the MIG sensors are ideally suited for space applications.

 

Scientific Imaging

The NDCDS ability offers two unique features for scientific imaging. First of all, the read noise can be practically removed by multiple readouts. Secondly, one does not need to maximize the Signal to Noise Ratio (SNR) by presetting the frame rate of the camera according to assumed movements in the scenery. Instead, full frame rate can be utilized while SNR is maximized by adjusting the frame rate afterwards according to the actual movements in the scenery.

 

MIG Pixel Structure

The Figure below illustrates a simple surface channel MIG transistor. In a real pixel one or two buried channel MIG transistors would be utilized in Back-Side Illuminated (BSI) image sensor configuration. The benefit of the MIG pixel is that it enables 100% fill factor, excellent quantum efficiency, as well as extremely low cross-talk and noise.

With only one transistor per MIG pixel one can achieve all the functionalities found in a standard 4 transistor CMOS image sensor pixel, namely, integration, selection, readout, and reset. If one additional transistor is included accurate non-destructive readout (NDCDS) is enabled.