German researchers have managed to develop a new generation of image sensors, which are more sensitive to light then their Silicon (Si) counter-parts and they come with an added bonus of being extremely simple and cheap to mass produce. The sensors consist of electrically conductive plastics which are sprayed on to the sensor surface as an ultra-thin layer. The chemical composition of the polymer spray coating can be altered enabling the invisible range of the light spectrum to be captured. Subsequently this brings about an interesting new development in terms of low-cost infrared sensors aimed at the compact cameras and smartphone industries. Please Note the results for the research, below, were published in Nature Communications 2012
Nowadays image sensors are the core component of every digital camera. In fact, before a snapshot appears on the display, the sensors firstly convert the light from the lens into electrical signals, and thereafter the image processor employs these to create the final photo.
Many compact / smartphone cameras consist of Si based image sensors mass manufactured by Complementary Metal Oxide Semiconductor (CMOS) technology. Researchers from Technische Universität München (TUM), Professor Paolo Lugli and Dr Daniela Baierl, have managed to develop a cost-effective process to markedly improve the performance of the CMOS sensors. Their methodology has evolved around an ultra-thin film made of organic compounds, typically known as plastics.
However, the challenge lay in applying the plastic solution on to the surface of the image sensors. The researchers extensively tested spin- and spray coating methods to apply the plastic in its liquid solution form as precisely and cost-effectively as possible. They were seeking a smooth plastic film which was no more then a few hundred nanometers in thickness. Therefore, spray-coating was found to be the optimum method by either using a spray gun or a spray robot.
Thin film coating with high sensitivity to light
Organic sensors have historically proven themselves in testing - typically three times more sensitive to light then conventional CMOS sensors, and the electronic components conceal some of the pixels, and, therefore, the photoactive Si surface.
Organic sensors can be easily manufactured without the expensive post processing step as typically required for CMOS sensors, which is applying micro lenses to increase the amount of captured light. Every part of every single pixel, including the electronics, is sprayed with the liquid polymer solution, thus, giving a surface that is 100% light sensitive. The low noise and high frame rate properties of the organic sensors also make them a good fit for cameras.
Potential for developing low cost infrared sensors
Another advantage of the plastic sensors is that the different chemical compounds can be employed to capture different parts of the light spectrum. For example, polymers, such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and/or
Poly (3-Hexylthiophene) (P3HT) are ideal for detecting visible light, and other organic compounds, such as squaraine dyes are sensitive to light in the near infrared (NIR) region.
As stated by Professor Paolo Lugli, Chair of Nanoelectronics at TUM - "By choosing the right organic compounds, we are able to develop new application that were too costly up until now," - and - "The future uses of organic infrared sensors include driver assistance systems for night vision and regular compact and cellphone cameras. Yet, the lack of suitable polymers is the main hurdle." Original article available here
As with similar type of nanoscopic coating studies, the future potential of nanotechnology has been handsomely sold. However, as stated previously, DCN Corp strongly believes it can compete by providing a cost-effective and efficient nano-fabrication process. Going forward, if you and/or your colleagues are interested in making DCN Corp's alternative process reality - please ensure to contact the company as soon as practicably possible.