Photonics Spectra Article -Time Delay Integration Speeds Up Imaging

May 2012

Using a sensor architecture that permits photoelectrons generated from multiple exposures to be summed with no additive noise enables high-speed imaging under light-starved conditions. This technology has become a standard in the automated inspection of flat panel displays and is expanding to markets such as photovoltaic panel inspection.

Time delay integration (TDI) imaging technology enables high-speed in-line automatic optical inspection (AOI) of high-performance displays such as those used in iPhones, iPads and high-definition televisions. The $130 billion flat panel display industry relies on TDI technology to ensure that every picture is perfect.

Recently, low-temperature polysilicon used for in-plane switching liquid crystal displays and organic LEDs has pushed pixels to very small dimensions. For example, the iPhone's Retina display has a density of 326 pixels per inch and a subpixel size of about 26 µm. The increasing density results in a demand for higher-speed and higher-resolution digital imagers that become increasingly light-starved and, in turn, need even higher responsivity. TDI technology is a proven solution that can meet these often conflicting demands.

New TDI products are increasingly capable of imaging beyond the visible range. The finer display structures have led to the use of light sources with shorter wavelengths down to the ultraviolet.

Concurrently, the solar panel industry is becoming more automated as it boosts production capacity. In-line inspection of silicon solar cells has low-illumination requirements, similar to those of flat panel display inspection. However, solar cells emit electroluminescent or photoluminescent photons with wavelengths around 1150 nm. Hence, solar cell inspection requires cameras that can detect near-IR photons.

Click here to read the full Photonics Spectra article by Teledyne DALSA's Xing-Fei He and Nixon O.