This page contains information on the AAO's science grade MIT/Lincoln Labs deep depletion 2Kx4K device - hereafter MITLL3. This is device W67c2 (chip 2 from wafer 67) of the CCID-20 format run fabricated at MIT/Lincoln Labs and packed on an AlN substrate by GL Scientific. It is a 2K x 4K edge-buttable device with 15 micron pixels. The wafer used was a high resistivity, or deep depletion, one. The pixels are 40 microns thick. It was first commissioned on the AAT in Oct 1998. The information provided is based on tests made at the Epping Lab by John Barton (a copy of his comprehensive report can be found here), observations made at the AAT with LDSS and the RGO spectrograph by C. Tinney and K. Glazebrook, and experience with MITLL3 use on UCLES.

MITLL3 cannot be binned in vertical or horizontal direction, due to hot columns which bleed charge into adjacent columns when binned.

Quantum Efficiency

The SiO AR coating used on this device is optimised for red performance. This, together with its thickness, produces an enhanced quantum efficiency longwards of 6000 Å. The quantum efficiency results shown for the MITLL3 below were obtained in the Epping lab, with the device being operated in diode mode. 


Wavelength (nm) 500 600 700 800 900 1000
Qauntum Efficiency (%) 61.3 80.6 86.9 82.5 58.6 15.9



Because the detecting layer is so thick this device has generally lower fringing than most thinned CCDs, while retaining excellent red sensitivity. The extent of fringing was explored using the MITLL3 on the 25cm camera of the RGO spectrograph with a 600R grating in October 1998. The following image shows a flatfield in the wavelength range 6400-9500Å normalised for the flat-field lamp's spectral response. Note that this image is just the 330x3200 pixel region illuminated by the RGO. 

  Gzipped Fits Image






These results show fringing on two seperate length scales: a large scale effect on scales of hundreds of pixels with 5% p-p amplitude at 9500 Å, and a small-scale effect on scales of 20 pixels (or 20 Å in wavelength) with 5% p-p amplitude at 9500 Å. This can be seen more clearly in the following cut through the above image made at Y=200-210 pixels. We see ±1.5% p-p at 8500 Å, ±4% at 9000 Å and ±5% at 9500 Å. The main result is that fringing is (1) negligible below 8000 Å, and (2) even above 8000 Å it is quite small.

















The device has a number of hot pixels, and one serious bright defect. With UCLES, appropriate set-up aligment can place it between an order.

The remaining hot pixels cause vertical trails in bias frames. In long dark frames several weaker hot pixels appear and become more prominent. The following images show bias and dark frames acquired approximately 9 hours after the CCD had been powered on.

The device shows a small number of trapping sites. The currently known locations of both bright defects and trapping sites are listed here.

BIAS Frame


NORMAL Speed created as median of 9 
frames. GIF Images are streched between 520 and 530 adu. 

Gzipped Bias fits file

DARK Frame 


Normal speed created as median of 5 
frames. GIF Images are stretched between 520 and 535adu 

Gzipped Dark fits file

Cosmic Rays

Because of the thickness of this device it seems to be very susceptible to cosmis rays. The observed hit rate for the entire detector is ~830 per 1000s. A particular point to note is that the cosmic rays are often seen to be quite extended. One hundred pixels is not uncommon. Moreover, cosmic rays are obviously interacting with the Si in this CCD to produce both curved trails and even small showers.


Dark Current

At 160K the dark current is small - a 2000 sec dark shows it was less than 0.4e-/pix/2000sec, once the CCD has been powered on for a day. However, the detector takes several days to reach this low a dark current level, due to a slow CCD cleanout rate. The CCD cleanout rate following power off and on, with a cold CCD, as measured in dark frames are:


Time after Power on
2 hours 
8 hours 
24 hours 
2-3 days 
 0.3 to 0.4 


Clock-induced Dark Currents are too week to be detected without binning, and since binning is not possible, can be ignored.



The UCLES camera optics cannot illuminate the entire area of the detector (which is 60 x 30mm in size). In fact the unvignetted region which can be observed is more like 38.5 x 18.8 mm (for less than 10% vignetting). The region covered at 50% vignetting is 60 x 34 mm, which is approximately the entire LL chip, however unless you are working in the very red, the echellogram will not put any light on much of the chip. 


The following sample images from ECHWIND show the region of the LL chip illuminated and the effects of vignetting.