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CMOS Flat Panel Detector v.s. Amorphous Silicon Flat Panel Detector

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Have you ever been confused about the difference between CMOS flat-panel detectors and amorphous silicon flat panel detectors?

X-ray imaging systems often use indirect flat-panel detectors to convert X-ray energy to light energy used to generate images of X-ray inspection. However, there are various options for these indirect types of flat panel detectors, each having its merits and demerits. Furthermore, careful consideration of these options can make a tremendous difference in choosing the proper detector for your unique X-ray inspection use case.

So, if you are ready to know more, then let’s dive in.


I. What is a CMOS Flat Panel Detector?

► Description 

Complementary Metal Oxide Semiconductor (CMOS) flat panel detectors have recently emerged into the X-ray imaging industry scene. These flat panel detectors have been projected as a good substitute for other types of indirect detectors. The reason is that they offer numerous benefits, including decreased image lags and higher frame rates. 

CMOS is an indirect flat-panel detector that can use small pixel sizes of less than 50 micrometers and fast readouts to assist high-resolution imaging systems in panels with small dimensions. They are also capable of low noise levels for readouts during signal detection. 


CMOS Flat Panel Detector


► Main Manufacturing Base

The main manufacturing base for CMOS flat-panel detectors has always been in the Asian continent, with Japanese and South Korean manufacturers taking the lead since they’ve had a long history of manufacturing imaging devices like SLR cameras and other digital imaging devices. 

Some Well-known Suppliers

Significant players in digital imaging devices such as Canon and Nikon have been the top suppliers of CMOS flat-panel detectors for a long time due to their long history of manufacturing imaging equipment. However, Chinese suppliers like Galaxy Core are gradually taking over a fair market share of CMOS detector supplies. Well-known suppliers include Omnivision, Samsung, Sony, Aptina, Galaxy Core, Canon, SiliconFile, and Toshiba. 


II. Advantages of CMOS Flat Panel Detector

CMOS X-ray imagers have seen an increase in popularity as an imaging device in the X-ray industry niche of small area X-ray imaging. This popularity is simply due to the advantages it offers, including 

  • There is a faster readout speed and reduced noise because of the much greater electrical charge movement in crystalline against amorphous silicon. Consequently, the lower noise offers a broader dynamic range in CMOS though the total pixel storage capacitance is similar as in Amorphous Silicon.  
  • Also, because the noise floor is shorter, the low dose Detective Quantum Efficiency (DQE) is considerably higher, and the X-ray detection in quantum noise is limited to very minimal dose levels. 
  • The faster readout speed provides quicker CT scanning, which is crucial for test samples requiring minimal exposure. 
  • In addition to the lower noise and higher speed, the pixel size can be lesser since the active crystalline silicon components are smaller than active amorphous silicon components. Furthermore, small pixels are beneficial for very high-resolution X-ray tomography purposes.


III. Disadvantages of CMOS Flat Panel Detector

While the CMOS flat-panel detectors offer numerous benefits, it falls short in specific technical areas. These disadvantage areas include

  • It has a higher sensitivity variation for the pixels, which often causes a more significant color noise. 
  • It also has a limited size. 
  • One other downside of the CMOS detector is the reduced radiation hardness. 
  • It also has a substantially lower fill factor with the effect of a decreased light sensitivity. 


IV. What is Amorphous Silicon Flat Panel Detector

► Description

Amorphous silicon (a-Si) detectors are a set of flat panel detectors that have been demonstrated to be the most appropriate semiconductor for large-area devices. These detectors come with a pixel pitch in the range of 200 μm as well as an active area of 20×20 square centimeters using one PIN switching diode and one PIN photodiode per pixel for readout. The scintillator used for these flat panel detectors is Cesium iodide which improves the performance of these detectors, making them more suitable than other flat panel detectors and are moving towards replacing existing flat panel detectors in radiographic X-ray systems. 


Amorphous Silicon Flat Panel Detector


► Main Manufacturing Base

The main manufacturing base of amorphous silicon flat panel detectors was the US until as recently as 2018. However, recent trends show that China is gradually taking over as the manufacturing base, seeing that production is significantly cheaper. The quality is at par with their American and European counterparts and even higher in some cases. 

► Some Well-known Suppliers

Recent development in the global X-ray imaging industry has seen some dynamic acquisitions and company mergers of some key players to put them in an advantageous position. One good thing is the increased developments and innovations spurred by the frequent competition among companies. 

Some of the well-known suppliers in the industry today include Uni X-ray, Varex Imaging Corporation, Agfa, FUJIFILM Holdings America Corporation, Troxell, and Canon. Other key players include Konica Minolta Business Solutions USA, Inc., Imaging Dynamics Company, Detection Technology, Hamamatsu Photonics UK limited, and Teledyne Technologies Incorporated. 


V. Advantages of Amorphous Silicon Flat Panel Detector

Amorphous Silicon flat panel detectors have been known to have numerous benefits that make them a desirable option for X-ray imaging components. Some of these benefits can be attributed to its component material, including its scintillator. These advantages include 

  • High conversion efficiency ensures that the X-ray energies are effectively converted to light energy to represent the test sample accurately.
  • It also has a wide dynamic range that makes it suitable for precisely capturing large test samples, a feat that other flat panel detectors often find challenging. 
  • Its high spatial resolution, which ensures that clear, high-quality images develop from the X-ray energy conversion, is another critical benefit. 
  • Amorphous Silicon flat panel detectors have high X-ray absorptivity in low-resolution areas due to their higher atomic number than amorphous selenium’s atomic number.
  • Finally, its environmental adaptability is vital.


VI. Disadvantages of Amorphous Silicon Flat Panel Detector

With all the numerous advantages that the Amorphous Silicon flat-panel detector offers X-ray imaging system operators, it is surprisingly not without its drawback even though they are minimal. The demerits of Amorphous Silicon flat panel detector can include

  • It has an inferior DQE (Detective Quantum Efficiency) to amorphous selenium at high doses.
  • Amorphous Silicon flat panel detectors have a slight scattering effect because of their fluorescence conversion layer. 
  • The sharpness in an Amorphous Silicon detector is relatively slightly reduced to that of an Amorphous Selenium FPD. 


VII. CMOS Flat Panel Detector vs. Amorphous Silicon Flat Panel Detector

  • Pixel

The CMOS utilizes active pixel image sensors, while Amorphous silicon detectors utilize charged-coupled image sensors. However, both are made from the same material, silicon, which gives them the same light sensitivities. 

  • Pixel Size

The CMOS has a smaller pixel size than amorphous silicon detectors. The effect of this factor is a faster pixel fill rate and a faster readout speed, and a decreased image lag time. 

  • Material

The difference in the manufacturing material is indicative of their unique performances. Amorphous Silicon detectors have scintillators made from cesium oxide for improved performance, while CMOS detectors are made from metallic oxides that ensure reduced noise levels during signal detection. 

  • Pixel Fill Rate

The fill rates are very different for both detector types, with CMOS having a faster fill rate than the Amorphous Silicon fill rate. This parameter is often dependent on the pixel size, which is smaller and faster for the CMOS detector. 

  • FPS

The FPS is a measure of the frame rate for the detectors. The CMOS has a higher frame rate than the Amorphous silicon detector, which gives it an advantage for faster image production. 



In conclusion, Amorphous silicon flat-panel detectors and Complementary Metal Oxide Semiconductor (CMOS) flat panel detectors serve X-ray imaging systems to produce high-quality, fast, and accurate images. However, these detectors have unique differences due to some unique parameters, making them suitable for specific use cases. These differences are also based on their advantages and disadvantages that you should consider carefully to make the right choice of flat panel detector for your X-ray inspection needs. 


Related Article: CCD vs CMOS – Which is Better?

Related Article: Industry X-Ray Vs. Medical X-Ray: What Is The Difference?

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