Performance and evaluation of large format 2Kx2K MBE grown HgCdTe Hawaii-2RG arrays operating in 32- channel mode G. Finger, R. J. Dorn, M. Meyer, L. Mehrgan, J. Stegmeier, A.F.M. Moorwood

Overview l Set-up »32 channel package using CMOS cryo-opamps instead of ASIC’s Test results with c =2.5  mHawaii2RG arrays »darkcurrent »QE »noise »Persistence »embedded reference pixels »Guide mode

Introduction Single Hawaii-2RG used for 1 array operating in integral field spectrograph SPIFFI ( c =2.5  m) 1 array in infrared spectrograph of X-shooter (1Kx2K needed, c =2.5  m) 3 arrays in K-band multiobject spectrograph KMOS ( c =2.5  m) 1 array in planet finder Mosaic of 2x2 2Kx2K Hawaii-2RG’s used for wide field imager Hawk-I ( c =2.5  m) l ASICS not yet available, CMOS cryo-opamps used instead l 32 –channels better than 4 channels on ground because frame time < 1 s lower readout noise better 1/f noise suppression with embedded reference pixels

32 channel package for Hawaii-2RG l 32 channel package without ASIC developed for ESO l Mosaic for Hawk-I and KMOS ? In collaboration with GL Scientific

32 channel package for Hawaii-2RG l Tip tilt and focus adjustment by 3 alignment screws l Detector cooled by cold finger on the backside of the array l Use of cryogenic CMOS preamplifiers cryogenic preamps Cold finger alignment screws epoxy support structure

32 channel package for Hawaii-2RG l Internal bus of array accessed directly by cryogenic CMOS amplifiers l Symmetric amplifier design for differential signal chain 32 video + 1 reference + 1 guide channel used in slow mode (100 KHz) l Bias and clock filtering at detector cryogenic preamps Cold finger

Thermal emission of cryogenic preamplifiers Heat-sinking of flex boards l Power dissipation of 68 CMOS cryo-opamps ~ 1W l Heater off detector on T=34.5K l Heater on detector off P=230 mW l proper thermal design and heat sinking of flex boards to instrument allows to heat sink 77 % of power to instrument 23 % of power to detector

Thermal emission of cryogenic preamplifiers l Power dissipation of 68 CMOS cryo-opamps ~ 1W l Heater off detector on T=34.5K l Heater on detector off P=230 mW l proper thermal design and heat sinking of flex boards to instrument allows to heat sink 77 % of power to instrument 23 % of power to detector l T detetor = 90K T cryo-opamp =150K l Supply voltage of opamp 6V : I dark = 0.1 e/s/pixel 3V : I dark = 0.1 e/s/pixel l Cryo-opamps do not increase darkcurrent as demonstrated with SPIFFI set-up Measured temperature 2.7  m 2.6  m 2.5  m 22 f/10

KMOS detector mount mechanical layout l Detector enclosure and preamplifier box have to be galvanically separated from instrument l Power dissipation of 68 CMOS cryo- opamps ~ 1W l Heatload on detector P=230 mW l For HawkI mosaic four preamplifier boards instead of ASIC’s Alignment screws Detector board & cryo preamp detector Micro-D 72 pin ronnectors at radiation shield Cooling braid

Mosaic Package l beautiful

Test results with c =2.5  m MBE 2Kx2K Hawaii-2RG arrays

Dark current versus temperature HgCdTe LPE / MBE LPE c =2.5  m ■ Hawaii2 2Kx2K □ Hawaii1 1Kx1K MBE c =2.5 / 1.7  m ▲ Hawaii-2RG 2Kx2K c =2.5  m ∆ PICNIC 256x256 c =1.7  m l MBE at T<80K I dark < 0.01 e/s/pixel l at T=100K I MBE =I LPE /1660 Good c =2.5  m MBE material can be used in liquid bath cryostats

Dark current versus temperature HgCdTe LPE / MBE LPE c =2.5  m ■ Hawaii2 2Kx2K □ Hawaii1 1Kx1K MBE c =2.5 / 1.7  m ▲ Hawaii-2RG 2Kx2K c =2.5  m ∆ PICNIC 256x256 c =1.7  m l MBE at T<80K I dark < 0.01 e/s/pixel l at T=100K I MBE =I LPE /1660 Good c =2.5  m MBE material can be used in liquid bath cryostats radiation background in SPIFFI

T=60K l Cut level -0.5/2 e/s/pix l Integration time 11 min

T=80K l Cut level -0.5/2 e/s/pix l Integration time 11 min

Detector operating temperature l for a perfect science grade array I dark < 0.01 e/s at T < 80 K l for a real array cosmetic quality improves if array cooled to T< 60 K l Required operating temperature depends on quality of science grade array

Quantum Efficiency 2.5  m MBE Hawaii-2RG l Hawaii2 LPE QE drops with temperature

Quantum Efficiency 2.5  m MBE Hawaii-2RG LPE Hawaii2 l Hawaii2 LPE QE drops with temperature l Hawaii-2RG MBE QE does not dependent on temperature l Science grade QE K-band: 0.84 H-band: 0.78 J-band: 0.71

Quantum efficiency versus wavelength l Smooth curve to obtain final result l Engineering grade using shot noise: K: 1.05 H: 0.81 J: 0.65 engineering grade

Conversion gain by capacity comparison method l Charge for resetting node capacity is provided by bias voltage Vreset

Conversion gain by capacity comparison method l add external relais and large external capacity C ext l charge for resetting node capacity is provided by C ext l eventually, after reading many frames, voltage across C ext will drop due to charge loss caused by resetting node capacity C 0 ( nframesx2Kx2K resets)

Quantum efficiency versus wavelength l Smooth curve to obtain final result l Engineering grade using shot noise: K: 1.05 H: 0.81 J: 0.65 engineering grade

Quantum efficiency versus wavelength l Smooth curve to obtain final result l Engineering grade using capacity comparison: K: 0.83 H: 0.64 J: 0.51 engineering grade

Quantum efficiency versus wavelength l Smooth curve to obtain final result l Engineering grade: K: 0.83 H: 0.64 J: 0.51 engineering grade

Quantum efficiency versus wavelength l Smooth curve to obtain final result l Engineering grade: K: 0.83 H: 0.64 J: 0.48 l Science grade K: 0.84 H: 0.78 J: 0.71 Z: 0.66 engineering grade science grade

Noise map of Hawaii-2RG c =2.5  m MBE array l Noise map for Hawaii-2RG l 13.4 erms on active pixels l 6.3 erms on reference pixels l Dominant noise source is IR pixel, not mux or acquisition chain l Clean set-up 4 columns of reference pixels on each side of the array

Readout Noise versus number of nondestructive readouts Fowler sampling: number of readouts n proportional to integration time: 825 ms/readout for 256 Fowler pairs 2.2 erms on IR pixels 1.3 erms on reference pixels scales to subelectron noise for Si-pin diodes ( HyVisi) shielding multiplexer glow very efficient: large number of nondestructive readouts possible with 32 channels

Readout Noise 256 Fowler pairs 2.5  m MBE Hawaii-2RG l 2.3 erms on active pixels l 1.3 erms on reference pixels

Glow centers l For large number of nondestructive readouts engineering grade arrays show glow centers l Fixed integration time 900s l Vary number of nondestructive readouts

Intensity of glow centers l Integration time 900 s l Glow proportional to number of nondestructive readouts l 27 pixels from center glow intensity is 61 e/frame

Glow centers l several isolated glow centers for large number of readouts on engineering array l No glow center on science array l Diffraction like ring structure l Selection criterium for science arrays l Hole in metal shield of MUX ?

Persistence l switch from LPE to MBE does not eliminate persistence l latent image can be seen for many hours l persistence on all arrays tested

Persistence l depends on fluence not on flux l N<N saturation =10 5 e no persistence l switch from LPE to MBE does not eliminate persistence l latent image can be seen for many hours l Threshold of persitence because of traps close to the pn junction ? 10 5 e

low frequency noise suppression with embedded reference pixels l Integration time 1.01 s l high frequency stripes in direction of fast shift register are 50 Hz pickup l Noise 45 erms l For each row subtract average of 8 embedded reference pixels on right and left edge of the array With 32 channels reference pixels are read twice every 420  s l Noise 24 erms l Linear interpolation of reference for each pixel using reference pixels of row and reference of subsequent row

Hawaii2GR in integral field spectrograph SPIFFI l Liquid bath cryostat T detector = 90 K c =2.5  m MBE Hawaii-2RG l Heat sinking of cables detector cooling braid Heat sink for clock video bias cables

Small Slicer 1 cm Large Slicer Pseudo Longslit 30 cm SPIFFI SPIFFI: SPectrometer for Integral Faint Field Imaging (MPE) Fully cryogenic spectrometer for the near infrared wavelength range from 1.0 – 2.5 µm Integral field unit with 32 x 32 pixels ra dec wavelength

Hawaii2RG in integral field spectrograph SPIFFI l K-band spectrum of Ne lamp l Slitlets staggered because of image slicer l Pixel scale 0.1 arcsec l FWHM = 1.4 pixels l Spectral resolution 6300

Hawaii2RG for Hawk-I l 1-2.5µm l All mirror optics l 4kx4k mosaic detector l 0.1” pixels 7.5x7.5’ field l Designed for possible use with adaptive secondary +laser guide stars

Guide mode for tip-tilt correction with LGS-AO sytem l Laser guide star AO system still need natural guide star for tip-tilt correction l use guide mode of Hawaii-2RG arrays for tip-tilt correction with NGS

Timing of guide window readout l Fowler or follow up-the-ramp sampling for science frame l Interleave guide window readout with full science frame readout l Guide window readout is nondestructive without reset: always subtract previous frame from new frame l only one read needed per double correlated image l Gain of 2 in bandwidth in comparison to read-reset read

Guide window read-reset-read l Window 16x16 l Star mag 9.5 l 256 windows per full frame

Guide window read-read-read l Window 16x16 l Star mag 14 l 64 windows per full frame l Frame rate 68 Hz l Guide window is not lost for science frame

IRACE 136 channel IRACE system similar system already operational for CRIRES

IRACE for Hawaii2RG 32-channel and guide window Add ADC board and 2 nd gigalink for guide window 2 ADC boards for 32 channels of science frame ADC board for guide window

IRACE for Hawaii2RG 32-channel and guide window Additional ADC board and 2 nd gigalink for guide window IRACE is flexible architecture covering all Applications Port flexibility to NGC Gigalink for 32 video channels of science frame Gigalink for guide window

IRACE for 2x2 mosaic of Hawaii2RG’s and guide mode l 136 channel system 16 bit 500 kHz 4x32 video channels 4x1 reference channels 4x1 guide window channels l Gigabit fiberlink l cryo-opamps instead of ASIC l Linux pc as number cruncher with home-made pci-bus gigalink interface

Conclusions l 32 channel setup with cryo-opamps operational at telescope l GL-scientific Mosaic package with128 channels for Hawk-I l QE high over the entire spectral range (K: 0.84, Z: 0.66) with correct PTF l With MBE dark current < 0.01 e/s at T< 80 K operation in LN2 bath cryostat possible, cosmetics improves at lower temperatures l Reference pixels eliminate drift and reduce pick-up: robust system l Readout noise double correlated sampling 13.4 erms on IR pixels 6.3 erms on reference pixels l Glow shielding on Hawaii-2RG efficient Readout noise with 256 Fowler pairs 2.2 erms on IR pixels 1.3 erms on reference pixels l Guide mode does not disturb science frame l Routine operation of Hawaii2RG in integral field spectrometer SPIFFI at the VLT with spectacular results on galactic center

The end

Spot scan Hawaii1 LPE array

Readout Noise versus number of nondestructive readouts Fowler sampling: number of readouts n proportional to integration time: 825 ms/readout for 256 Fowler pairs 3 erms on IR pixels 1.8 erms on reference pixels scales to subelectron noise for Si-pin diodes ( HyVisi) shielding multiplexer glow very efficient: large number of nondestructive readouts possible with 32 channels STScI

Quantum efficiency versus wavelength l Smooth curve to obtain final result l Engineering grade using shot noise: K: 1.05 H: 0.81 J: 0.65 engineering grade

Guide window read-read-read l Window 16x16 l Star mag 14 l 256 windows per full frame l Frame rate 143 Hz l Guide window is not lost for science frame

Comparison of cosmetic quality 40K / 80 K Cut levels -250 e /200 e, DIT 900 sec T=40 K T=80 K

Integral field spectroscopy l optically slice image l align slices on slit of spectrometer l take spectrum for each pixel in 2dimensional image