FLAT PANEL DISPLAYS
and it needs a lot of improvements, for example an increased contrast ratio of the polarisation filters, but we think that this will be a trend in the future that imaging will be going through.’
Three fields, one capture Because of the size of potential display defects decreasing with pixel size, according to He the traditional imaging methods previously used to detect display defects are no longer relevant, and because of this the industry is moving to a new technique, multi-field imaging. ‘Display manufacturers have previously
been required to use bright field, dark field and back light images to inspect certain defects in displays,’ He said. ‘Previously, these images had to be captured in three separate scans, which took a relatively long time to do, making it more difficult to meet the time restrictions of the production line.’ For this reason, the Linea ML line scan
camera launched by Teledyne Dalsa last year – in addition to its upcoming Linea HS TDI line scan camera – has been designed to capture bright field, dark field and back light images in a single scan, which speeds up FPD inspection. ‘Multi-field imaging is enabled by using
either time division or wavelength division. Here, a special coating on silicon creates a colour filter that separates different wavelengths, which have different lighting angles, and that are used to capture the three different types of image,’ explained He. ‘Te challenge with multi-field imaging, however, is that because all three types of image are captured at the same time, a higher level of data throughput is required to process them in the reduced time frame enabled by using the technique.’ To meet the increased data throughput
The perfect diamond structure of this OLED screen of a Samsung Galaxy can be seen after being captured using a 151-megapixel camera from Vieworks
requirements of multi-field imaging, Teledyne Dalsa developed Camera Link HS, which incorporates fibre optics. Te high-speed interface enables the Linea ML and upcoming Linea HS camera to transmit data at 5GB/s, according to He, approximately six times faster than the data transfer enabled by the traditional Camera Link interface. Multi-field imaging is a feature offered by
Vieworks’ TDI cameras, with the firm planning to release a system in 2020 equipped with it.
Going micro An interesting development in the consumer display market has been the emergence of micro-LEDs, a technology poised to rival OLEDs and QLEDs that Samsung demonstrated at the Consumer Electronics Show two years in a row – first as a 146-inch display called Te Wall in 2018, then a 75-inch television display. Pixels based on micro-LEDs consist of arrays
Vieworks’ VC-155 camera offers 155-megapixel resolution and a wide field of view, enabling it to capture an entire phone display in a single image
of microscopic LEDs forming each individual pixel element. As is the case with OLED pixels, micro-LED pixels produce their own light – rather than requiring a backlight such as those found in LCDs – meaning they are able to achieve the perfect black levels currently associated with OLEDs. Tey can also do this without the danger of burn-in – an issue that has plagued OLED displays since their arrival, where persistent images on-screen remain faintly in the background even aſter the image changes. In addition, micro-LEDs have been shown to deliver a longer lifetime than OLEDs, a higher brightness than any current display technology, a wide colour gamut, all while avoiding issues regarding viewing angle and uniformity faced by LCDs.
20 Imaging and Machine Vision Europe • August/September 2019 While the technology shows promise, and
despite Samsung having announced it will offer micro-LED displays to the home luxury market by the end of the year, the technology is still in its infancy. As to how the emergence of this potentially
Every new
technology brings with it new challenges... until now, the resolution hasn’t been so challenging
disruptive technology might affect the demands placed on imaging technology used to inspect it, even with the new pixel structure, He, of Teledyne Dalsa, doesn’t believe there will be a significant change. ‘Te pixel size might get smaller, and the type of defect might be different, but in terms of inspection I don’t see it needing a specific technique,’ he said. Teledyne Dalsa does
currently have some customers inspecting micro- LED displays. However, these are large displays intended for outdoor use, such as advertising, rather than in
smaller devices for consumer use. Te pixels of these displays are also much larger than those that would be used in televisions, phones or tablets. Lewis, from InZiv, had a slightly different
opinion: ‘Every new technology brings with it new challenges. When the semiconductor industry went from the microscale to the nanoscale, a whole new field of tools were needed to deal with that. I think we’re starting to see the same transition occur in the display industry, but up until now, the resolution hasn’t been so challenging that this was really a strong issue.’ He added that the same aspect that makes
InZiv’s solution valuable to the OLED industry – the ability to give a wide variety of information at the nanometre scale – will make it equally important for micro-LEDs. O
@imveurope
www.imveurope.com
Vieworks
Vieworks
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