Industry-wide Change to Complementary Metal Oxide Semiconductors (CMOS)
There are many reasons the industry is shifting to the CMOS arrays, but this decision is due, in part, to the differences in manufacturing processes between the two styles of detector. While the CMOS detector array can be manufactured on a standard semiconductor assembly line like most microprocessors, the CCD detector requires specialized processes. These processes are credited with CCD’s historic reputation for low-noise, high-sensitivity instruments, but are a manufacturing disadvantage.
Both the CCD and CMOS detector arrays perform the same essential photoreactive function. They take light and turn it into electrical impulses capable of being decoded into a signal or image. The main difference lies in what these detector arrays do with the charge created by light striking the pixels of the array.
The special manufacturing process for the Charged Coupled Device allows the charge from each pixel to be moved across the chip then is read from one corner of the pixel array in sequence. Historically, this single point of contact for the reading allowed the CCD array to create very high-quality, low-noise images. This method requires a longer integration time, however. With a 2048 pixel array, a CCD typically requires a minimum of 1-2 ms to integrate.
Advantages of CMOS over CCD
Complementary metal-oxide semiconductor (CMOS) detector arrays are manufactured using the same processes as other semiconductor chips, giving the CMOS a manufacturing advantage. This process places a transistor alongside each pixel to amplify and move the charge directly, rather than transporting the charge and queueing the data at a single point. Because data transfers from each pixel, rather than being queued to read in sequence, the processing time is orders of magnitude faster for a CMOS detector.
The unique flexibility of the CMOS detector’s direct charge conversion, in addition to providing processing speed advantages, also eliminates blooming and smearing that are a weakness of the CCD arrays. These advantages for the CMOS, coupled with the onboard processing power of Avantes’ newest AS7010 electronics board in the EVO series, allow for improved signal-to-noise and superior control through native USB3.0 and Gigabit ethernet communication.
The AvaSpec-ULS2048CL-EVO operating from 200 nm to 1100 nm, with a resolution as low as 0.06 nm full-width half-maximum (FWHM), achieves integration times as fast as 30a00µs with a 2048 pixel array CMOS detector. This better supports high-speed applications such as pulsed source measurements, laser-induced breakdown spectroscopy (LIBS), and laser characterization.The dynamic range capabilities of the CMOS detectors is another advantage with improved native UV response from 200 to 400 nm and greater near-infrared sensitivity above 900nm.
Advancements in CMOS
Complementary metal-oxide semiconductor (CMOS) technology has advanced in recent years, and with manufacturers focusing on development, we can expect the rate of advancement will only increase in the near future. Recent improvements in resolution, quantum efficiency, and noise characteristics have already raised CMOS detectors capabilities to surpass the performance of CCD arrays in many cases.
As CMOS technology matures, Avantes expects to adopt more of this technology across our spectrometer platform. We are expanding product compatibility while continuing to provide products and support for CCD devices through 2020.
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Reasons to choose a CMOS detector array
For some applications, the CCD detectors will remain the first choice of researchers and industry experts, however, with frequent advancement in CMOS technology, the new detectors are favored for a growing number of uses.
The 30µs integration time and short external trigger delay (0.9µs) makes the CMOS a win for high-speed applications like laser induced breakdown spectroscopy (LIBS) and pulsed source radiometry.
Avantes is currently offering CMOS detectors in the AvaSpec-ULS2048CL-EVO, part of the new EVO series of spectrometers featuring the next generation in electronics, and the ULSi Integrated Microspectrometer for OEM applications.
Additionally, Avantes continues to offer a wide variety of high-performance, back-thinned CCD detectors in our Sensline product family. These detectors are optimized for signal to noise over speed in most cases, however, they also feature native UV response and solid NIR quantum efficiency as compared with typical front-illuminated CCD detectors.