Viewpoint: Industrial imaging
Lou Hermans, COO at Cmosis, sees growing demand for image sensors optimised for UV and NIR wavelengths
T
he demand for very high-resolution area image sensors for machine vision applications is expected to continue to grow.
Tis growth is mainly fuelled by the expanding need for inspection of LCD panels used in smart phones, tablets and TVs. Tese screens are not only becoming bigger, but also the resolution is continuously increasing. Tis combination is at the basis of the demand for 50+ megapixel resolution inspection cameras and image sensors. Frame rate requirements are in the 10 frames per second range – out of reach of most CCD-based camera solutions. Although most camera users and producers would prefer global shutter- based CMOS solutions, a fair amount of these applications can also be realised with rolling shutter type pixel-based image sensors. Te increase in resolution also pushes for
smaller pixel sizes in order to keep the overall image sensor size within reasonable limits. Sensor size not only defines the price of the imager but also the cost of the lenses to be used with these imaging devices. Te realisation of smaller, high-performance global shutter pixels will remain a challenge. It implies that image sensor
manufacturers have to migrate to more advanced and more expensive CIS process technologies. I also expect a growing demand for image
sensors optimised for wavelengths outside the visible spectrum, more in particular for the capture of UV and NIR images. UV imaging is mainly driven by the needs of the semiconductor industry whereas NIR imaging is by non-obtrusive machine vision applications. I expect that the demand for UV sensitive imagers will accelerate the development of backside-thinned and illuminated CMOS image sensors in industrial and professional applications. Although backside illuminated imagers are now the standard in mobile phone camera applications, they are still the exception in machine vision area. Te larger pixels of machine vision imagers do not benefit much in terms of QE increase in the visible when using backside illumination. Te limited performance increase cannot justify the significantly higher price. For UV however, the QE increase is significant and customers are
The realisation of smaller, high- performance global shutter pixels will remain a challenge
willing to pay the higher price. Te introduction of backside illuminated devices in industrial cameras is also delayed because few foundries are ready to support backside thinning and processing for such low-volume applications. For the same reasons, I do
not expect to see so-called stacked backside illuminated CMOS image sensor technology to be applied shortly in dedicated machine vision image sensors. Tis technology,
using separate pixel and logic wafers, bonded and interconnect, allows the use an optimal process technology for each separate layer and is very interesting for imagers having a large logic part as found in system-on-chip or SoC imaging devices. On the other hand, we expect to see more of
SoC imaging devices in the larger volume and lower end machine vision applications. But these will very likely be manufactured in the classic planar technologies.
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www.imveurope.com
Nicholas James, imaging product line manager at Edmund Optics, comments that with higher performance image sensors coming onto the market, lens choice to optimise those sensors will be increasingly important
I
n the past year imaging and automation customers have been adopting larger, higher- resolution sensors. One-inch format sensors
have become more readily available, and the machine vision industry is moving toward four- and six-megapixel resolution versions of these larger sensors. Te market will continue to push upward toward the nine- and 12-megapixel options – and even higher as technology evolves. Many lenses currently on the market are optimised for use with sensors of 2/3-inch or smaller. Tese lenses will typically vignette (darken the corners) on one-inch format sensors, so it’s important optics are selected that are designed to take advantage of the one-inch sensors. It’s not only the larger format that presents a
lens design and manufacturing challenge. Optics manufacturers must also be certain the lenses
To maximise
performance, multiple lens options should be evaluated and tested
provide high contrast on ever-smaller pixels. Lenses designed before the recent ‘renaissance’ of one-inch format sensors were typically only intended for two- to four-megapixel resolution. Many of these older designs will not maintain the contrast needed to maximise the performance of today’s smaller- pixel sensors; on the scale of today’s sub-5µm pixels these lenses will blur the image features that higher-resolution sensors are designed to resolve. To maximise performance,
multiple lens options should be evaluated and tested. A high-resolution, large-format sensor won’t produce high-
quality images without a lens that can match its resolution. It’s not always feasible to physically test multiple lenses – but Edmund Optics, for example, can provide simulations detailing how a specific product will perform in an application.
16 Imaging and Machine Vision Europe • Yearbook 2014/2015 Te growing use of
high-megapixel, one-inch sensors, the availability of high-quality lenses designed to optimise that sensor performance, and the recent rise in USB 3.0 as an imaging standard have combined to enable customers to collect, analyse, and use more information than ever before. Te trend will continue into 2015, and I fully expect sensor manufacturers to release even higher resolution products into the marketplace. Tis will make it even more important for vision system designers to choose lens options that are optimised to take full advantage of the higher resolution and maximise the amount of usable information that can be pulled out of a captured image. I look forward to these developments as they
continue to increase the potential applications, allowing opportunities that were once too complicated and cost-prohibitive to fully utilise industrial imaging.
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