e2v Presentation

Presentation for e2v second round interview - CCDs

Transcript

1. An Introduction to CCD’s Dr. James Finn
2. Outline  What is a CCD?  Physics of a CCD  Device Operation  Key performance parameters:  Quantum Efficiency  Dark Current  Concluding Remarks
3. + Charge Coupled Device (CCD) + Semiconductor based device + Array of p-doped Si pixels + Convert incident photons to electronic charge What is a CCD? ➲ Astronomical ➲ Space and Earth Observation ➲ Life Sciences ➲ Fast lifetime fluorescing ➲ Scientific ➲ X-Ray spectroscopy ➲ Health Care ➲ Dental X-Rays ➲ Ophthalmology CCD231-84 Hubble Telescope
4. e- Conduction Band Valence Band h+ Physics of a CCD + Semiconductor Physics + Two types of doped semiconductors: + P-type (excess holes) + N-type (excess electrons) + Photon incident to CCD + Excitation of electron across energy band-gap + Creation of an exciton (electron- hole pair) at semiconductor interface
5. SiO2 p-Si substrate ħν Gates substrate + Positive voltage bias through gates + n-channel formed beneath gates + Excitons formed in n-channel + Electrons and holes separated by electric field + Holes to substrate + Electrons to surface + Formation of depletion region Device operation +V V V n-Channel
6. substrate Device operation +V +V V substrate +V V substrate +V +V V V + Positive voltage bias through gates + n-channel formed beneath gates + Excitons formed in n-channel + Electrons and holes separated by electric field + Holes to substrate + Electrons to surface + Formation of depletion region + Charge in wells moved along row alternating voltage on gates + Moved to IC to be manipulated
7. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise
8. CCD Key performance parameters Ratio of induced current to incident flux. + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Number of photons converted to charge in the pixel.
9. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Wavelength (nm) Quantum Efficiency (%) Range of wavelengths absorbed by the CCD and QE obtained. Change of coating will change the spectral response.
10. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Output Current Photo- generation pairs Depletion Region pairs Surface pairs Neutral Bulk pairs Sources of additional Charge “noise” Reduced through cooling
11. CCD Key performance parameters Maximum frequency rows can be read from the CCD array Effective frame-rate of the camera + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise
12. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Measure of the transfer characteristic of the CCD output.
13. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Maximum signal which can be stored, transferred and read from a pixel in the CCD. Can be determined through saturation of the pixel well, or other specified limit
14. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Measure of ability to determine maximal difference between dark/light limits. Ratio of maximum possible signal (full well) vs. the total noise signal (in the dark)
15. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise Range of wavelengths of photons that can be converted to charge. Areas of application for the CCD
16. CCD Key performance parameters + Quantum Efficiency + Spectral Response + Dark Current + Maximum Readout Freq + Output Responsivity + Peak Signal + Dynamic Range + Spectral Range + Readout Noise A measure of the additional charge “noise” (Dark Current) added to the output frame. Removed through ‘Dark Frame’ subtraction and additional cooling.
17. CCD Tailoring + Dark Current Reduction through cooling + Liquid Nitrogen + Peltier based coolers + CCD coating to change spectral response/QE + Readout frequency can be increased through the use of on chip charge storage + Increased Resolution + QE increased through Back- Illumination fabrication Other e2v Imaging Systems: • CMOS • L3VISION
18. Overview  Discussed semiconductor physics  CCD device operation methods  Key performance parameters  Quantum Efficiency  Dark Current  Spectral Range/Response  CCD’s can be tailored for their application
19. Thanks for Listening. Images and spectral response graph attributed to e2v. Hubble image by NASA.