Abstract

J. J. Díaza, F. Gagoa, C. González-Fernándeza, Francis Beigbederc, F. Garzóna,b, J. Patróna

a Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna (Tenerife) SpainPhone: 34922605200, Fax: 34922605210, e-mail address: [email protected]

b Departamento de Astrofísica, Universidad de La laguna (Tenerife) Spainc Observatoire Midi-Pyrénées (OMP), France

EMIR is a multiobject intermediate resolution near infrared (1.0-2.5 microns) spectrograph with image capabilities to be mounted on the 10m Gran Telescopio Canarias (GTC), located on the Spanish island of La Palma.The instrument uses an Hawaii-2 infrared detector. In this paper, results of the detector characterization are presented. Apart from tests to obtain the typical figures of merit, such as readout noise, well depth, dark current, quantum efficiency or maximum pixel rate, some detailed studies have been performed to characterize the detector persistence, crosstalk between channels and the disturbing effects that appear in these detectors just after reset or after a certain time without being read. These effects and the techniques we have tried to minimize them are also presented.

Abstract

Hardware configuration

Q u a d r a n t W i n d o w G a i n ( e - / A D U )

1 ( 6 0 0 , 6 0 0 ) - ( 8 9 9 , 8 9 9 ) 2 . 3 5

2 ( 1 6 0 0 , 6 0 0 ) - ( 1 8 9 9 , 1 8 9 9 ) 2 . 3 3

3 ( 6 0 0 , 1 6 0 0 ) - ( 8 9 9 , 1 8 9 9 ) 2 . 4 3

4 ( 1 6 0 0 , 1 6 0 0 ) - ( 1 8 9 9 , 1 8 9 9 ) 2 . 4 4

T h e S y s t e m G a i n ( e / A D U ) w a s c o m p u t e d i n d e p e n d e n t l y i n 4 s e c t i o n s c o r r e s p o n d i n g t o d i f f e r e n t q u a d r a n t s . A s t h e e l e c t r o n i c c h a i n i s i d e n t i c a l f o r e v e r y c h a n n e l t h e r e s u l t i s u s e d t o e x p l o r e f o r u n b a l a n c e d g a i n i n d i f f e r e n t a r e a s o f t h e d e t e c t o r .

G a i n t e s t r e s u l t s f o r d i f f e r e n t a r e a s o f t h e d e t e c t o r .

S y s t e m G a i n

N o r m a l i z e d D e t e c t o r g a i n

The operational amplifier in the fan-out, the OPA350, is a single-supply rail-to-rail amplifier working between 0 and 5 . Its behaviour at cryogenic temperatures (77 K) is adequate for this application and it has proven to be reliable and repetitive after many thermal cycles. (See Poster by F. Gago et al. in this conference)

Cold Preamplifier Stage. (4 Channel configuration)

Fan-Out. 4 Channels.

Fan-Out. 32 Channels. Flat Flex circuits are used instead of cables

An unexpected behaviour was identified after a period of detector output inactivity.Subtracting two consecutive images, obtained immediately after a long period of integration, showed a bizarre effect in the first pixels of every channel. This effect has been identified as transient effect of the detector outputs until a temperature stable regime is reached.The picture shows the result of subtrating the two images. As it can be seen the temperature stabilization occurs while the first lines are read. After long periods of integration a dummy read has to be done to avoid this effect.

Test Conditions

Preamplifier offset voltage = 3.5 V Vreset = 0.5 V Biasgate = 3.7 V Cryostat cover closed. Filter also in closed position. T = 77K

Image acquisition sequence

10 consecutive Reset cycles of the whole detector Acquisition of 6 consecutive images Wait for 10 minutes Acquisition of 6 consecutive images

Dark Current. Noise

Signal variation due to Detector output thermal instability

Once the thermal transient of the outputs of the detector has finished, a much more stable output is appreciated. As it can be seen in the picture at the right, the detector shows a flat response for almost all the sensible area. Bad pixels affect the calculation statistics and appear in the figure as spikes.The mean values obtained for the dark current are approximately 0.12 e/sec. This figure has to be considered carefully as a strong dependence of the dark current with time has been observed when the detector was previously saturated.

Dark current 3-D histogram

The Reset value depends on the previous saturation state of the Detector. This is the case illustrated in the picture above showing the result of a persistency effect specially remarkable in one of the corners of the detector.

Signal value at Reset after saturation1st image and

time (t1) 2nd image and

time (t2)

Elapsed time (t2 – t1) in seconds

Difference in ADUs and electrons

Mean dark current in e- / s

Oscuridad_2_2 (691s)

Oscuridad_3_2 (1360 s)

669 123 / 295 0.44



668 82 / 197 0.29



669 63 / 151 0.23



669 51 / 122 0.18



668 44 / 106 0.16



669 39 / 94 0.14



669 33 / 79 0.12



668 31 / 74 0.11



668 28 / 67 0.10

A variation of the Dark current versus time has been observed. The picture at right shows two graphs with the evolution of the dark current with time. Different profiles correspond to different values of saturation before Resetting the Detector Charge to start with the measures. The higher the charge before the Reset, specially if the detector enters the saturation regime, the higher the initial Dark current.

Dark current versus time

The Dark files has been used to compute the Detector noise. The mean noise value is 11 electrons.

T h e d e t e c t o r w a s i l l u m i n a t e d w i t h a b l a c k b o d y . T h e f l u x r e c e i v e d o n t h e d e t e c t o r f o r s e v e r a l f i l t e r s h a s b e e n m e a s u r e d a n d c o m p a r e d w i t h t h e t h e o r e t i c a l o n e t o c a l c u l a t e t h e r e l a t i v e q u a n t u m e f f i c i e n c i e s a t d i f f e r e n t w a v e l e n g t h s . T h e t e s t i s p e r f o r m e d a t 2 d i f f e r e n t t e m p e r a t u r e s ( 8 0 0 º C a n d 9 8 0 º C ) t o v a l i d a t e t h e r e s u l t s .

R e l a t i v e Q u a n t u m e f f i c i e n c y .

R e l a t i v e Q u a n t u m e f f i c i e n c y

F i l t e r s P a s c h e n B e t a / H 2 0 . 6 3

H / H 2 0 . 9 4

L i n e a r i t y 2 %

c o n s i d e r i n g 1 s t p i x e l i n r a m p

L i n e a r i t y 2 % n o t


L i n e a r i t y 5 % c o n s i d e r i n g 1 s t p i x e l i n r a m p



F u l l w e l l

Q u a d r a n t 1 1 1 5 0 0 0 1 2 1 5 0 0 1 2 1 5 0 0 1 2 1 5 0 0 1 2 7 5 0 0 Q u a d r a n t 2 1 1 5 0 0 0 1 1 9 0 0 0 1 1 9 0 0 0 1 1 9 0 0 0 1 2 7 5 0 0 Q u a d r a n t 3 1 1 7 6 6 7 1 2 7 0 0 0 1 2 7 0 0 0 1 2 7 0 0 0 1 3 3 5 0 0 Q u a d r a n t 4 1 1 5 0 0 0 1 2 4 0 0 0 1 2 4 0 0 0 1 2 4 0 0 0 1 3 1 7 5 0

T h e D e t e c t o r w a s i l l u m i n a t e d w i t h a s t a b l e B l a c k B o d y a n d u n i f o r m l y o v e r i t s s u r f a c e . T h e c o n t r i b u t i o n i n t h e l i n e a r r e g i m e w a s o b t a i n e d u s i n g a 2 % a n d 5 % l i n e a r i t y c r i t e r i a . A l s o t h e F u l l W e l l w a s c o m p u t e d a s t h e t o t a l c h a r g e e v e n c o n s i d e r i n g t h e s i g n a l s a t u r a t i o n z o n e .

W e l l d e p t h a n d f u l l w e l l r e s u l t s .

W e l l d e p t h . F u l l w e l l

To perform the persistency tests the Detector is initially saturated. It is exposed to the laboratory radiation during 1 minute with no filter placed and then it is covered with a cool blank. A series of images P1, P2, P3 etc is taken as describedP1: Immediately after saturation, 1 reset cycle is made followed by 4 readouts,a 10 minutes wait and other 4 readouts. So P1 is: 1 reset, 4 readouts, 10’, 4 readouts. Following this scheme:P2: 2 resets, 4 readouts, 10’, 4 readoutsP3: 3 resets, 4 readouts, 10’, 4 readouts and so on.As can be seen in the picture the behaviour is different due to the need to repeat the Reset cycle to remove the effect associated to the initial saturation. Also, a dark current increase is associated to the previous saturation of the detector.

Detector response after saturation. Dark current vs saturation

Saturation vs non saturation.

The figure compares the behaviour of two different areas of the detector. The blue graph corresponds to a previously saturated area while the red one has not been saturated before the measurements. As it can be seen the Dark Current is strongly dependent and is a remarkable persistency effect.

Persistency

Q uadrant #1 Q uadrant #2 Q uadrant #3 Q uadrant #4

M inim um difference value

considered as ok ( - 4)

18272 16417 19134 16536

M axim um difference value

considered as ok ( + 4)

45858 36660 50181 43358

Cold pixels 524 (0.05%) 633 (0.06%) 291 (0.03%) 225 (0.02%)

H ot pixels 0 57 (0.005%) 0 11 (0.001%)

Dead_0_0 483 (0.05%) 65 (0.006%) 527 (0.05%) 122 (0.01%)

Dead_65535_65535 161 (0.02%) 435 (0.04%) 0 0

O ther_dead 6 (0.0006%) 14 (0.001%) 0 2 (0.0002%)

Total bad pixels 1174 (0.11%) 1204 (0.11%) 818 (0.08%) 360 (0.03%)

Pixels have been grouped in different categories according to their response to illumination. The table shows the criteria and the number of pixels in each category.

Bad pixel distribution

Detector Cosmetics

Q u a d r a n t W i n d o w G a i n ( e - / A D U )

1 ( 6 0 0 , 6 0 0 ) - ( 8 9 9 , 8 9 9 ) 2 . 3 5

2 ( 1 6 0 0 , 6 0 0 ) - ( 1 8 9 9 , 1 8 9 9 ) 2 . 3 3

3 ( 6 0 0 , 1 6 0 0 ) - ( 8 9 9 , 1 8 9 9 ) 2 . 4 3

4 ( 1 6 0 0 , 1 6 0 0 ) - ( 1 8 9 9 , 1 8 9 9 ) 2 . 4 4

T h e S y s t e m G a i n ( e / A D U ) w a s c o m p u t e d i n d e p e n d e n t l y i n 4 s e c t i o n s c o r r e s p o n d i n g t o d i f f e r e n t q u a d r a n t s . A s t h e e l e c t r o n i c c h a i n i s i d e n t i c a l f o r e v e r y c h a n n e l t h e r e s u l t i s u s e d t o e x p l o r e f o r u n b a l a n c e d g a i n i n d i f f e r e n t a r e a s o f t h e d e t e c t o r .

G a i n t e s t r e s u l t s f o r d i f f e r e n t a r e a s o f t h e d e t e c t o r .

S y s t e m G a i n

N o r m a l i z e d D e t e c t o r g a i n

An unexpected behaviour was identified after a period of detector output inactivity.Subtracting two consecutive images, obtained immediately after a long period of integration, showed a bizarre effect in the first pixels of every channel. This effect has been identified as transient effect of the detector outputs until a temperature stable regime is reached.The picture shows the result of subtrating the two images. As it can be seen the temperature stabilization occurs while the first lines are read. After long periods of integration a dummy read has to be done to avoid this effect.

Test Conditions

Preamplifier offset voltage = 3.5 V Vreset = 0.5 V Biasgate = 3.7 V Cryostat cover closed. Filter also in closed position. T = 77K

Image acquisition sequence

10 consecutive Reset cycles of the whole detector Acquisition of 6 consecutive images Wait for 10 minutes Acquisition of 6 consecutive images

Dark Current. Noise

Signal variation due to Detector output thermal instability

Once the thermal transient of the outputs of the detector has finished, a much more stable output is appreciated. As it can be seen in the picture at the right, the detector shows a flat response for almost all the sensible area. Bad pixels affect the calculation statistics and appear in the figure as spikes.The mean values obtained for the dark current are approximately 0.12 e/sec. This figure has to be considered carefully as a strong dependence of the dark current with time has been observed when the detector was previously saturated.

Dark current 3-D histogram

The Reset value depends on the previous saturation state of the Detector. This is the case illustrated in the picture above showing the result of a persistency effect specially remarkable in one of the corners of the detector.

Signal value at Reset after saturation1st image and

time (t1) 2nd image and

time (t2)

Elapsed time (t2 – t1) in seconds

Difference in ADUs and electrons

Mean dark current in e - / s

Oscuridad_2_2 (691s)


669 123 / 295 0.44



668 82 / 197 0.29



669 63 / 151 0.23



669 51 / 122 0.18



668 44 / 106 0.16



669 39 / 94 0.14



669 33 / 79 0.12



668 31 / 74 0.11



668 28 / 67 0.10

A variation of the Dark current versus time has been observed. The picture at right shows two graphs with the evolution of the dark current with time. Different profiles correspond to different values of saturation before Resetting the Detector Charge to start with the measures. The higher the charge before the Reset, specially if the detector enters the saturation regime, the higher the initial Dark current.

Dark current versus time

The Dark files has been used to compute the Detector noise. The mean noise value is 11 electrons.

Q uadrant #1 Q uadrant #2 Q uadrant #3 Q uadrant #4

M inim um difference value

considered as ok ( - 4)

18272 16417 19134 16536

M axim um difference value

considered as ok ( + 4)

45858 36660 50181 43358

Cold pixels 524 (0.05% ) 633 (0.06% ) 291 (0.03% ) 225 (0.02% )

H ot pixels 0 57 (0.005% ) 0 11 (0.001% )

Dead_0_0 483 (0.05% ) 65 (0.006% ) 527 (0.05% ) 122 (0.01% )

Dead_65535_65535 161 (0.02% ) 435 (0.04% ) 0 0

O ther_dead 6 (0.0006% ) 14 (0.001% ) 0 2 (0.0002% )

Total bad pixels 1174 (0.11% ) 1204 (0.11% ) 818 (0.08% ) 360 (0.03% )

Pixels have been grouped in different categories according to their response to illumination. The table shows the criteria and the number of pixels in each category.

Bad pixel distribution

Detector Cosmetics

L i n e a r i t y 2 %




L i n e a r i t y 5 % c o n s i d e r i n g 1 s t p i x e l i n r a m p



F u l l w e l l

Q u a d r a n t 1 1 1 5 0 0 0 1 2 1 5 0 0 1 2 1 5 0 0 1 2 1 5 0 0 1 2 7 5 0 0 Q u a d r a n t 2 1 1 5 0 0 0 1 1 9 0 0 0 1 1 9 0 0 0 1 1 9 0 0 0 1 2 7 5 0 0 Q u a d r a n t 3 1 1 7 6 6 7 1 2 7 0 0 0 1 2 7 0 0 0 1 2 7 0 0 0 1 3 3 5 0 0 Q u a d r a n t 4 1 1 5 0 0 0 1 2 4 0 0 0 1 2 4 0 0 0 1 2 4 0 0 0 1 3 1 7 5 0

T h e D e t e c t o r w a s i l l u m i n a t e d w i t h a s t a b l e B l a c k B o d y a n d u n i f o r m l y o v e r i t s s u r f a c e . T h e c o n t r i b u t i o n i n t h e l i n e a r r e g i m e w a s o b t a i n e d u s i n g a 2 % a n d 5 % l i n e a r i t y c r i t e r i a . A l s o t h e F u l l W e l l w a s c o m p u t e d a s t h e t o t a l c h a r g e e v e n c o n s i d e r i n g t h e s i g n a l s a t u r a t i o n z o n e .

W e l l d e p t h a n d f u l l w e l l r e s u l t s .

W e l l d e p t h . F u l l w e l l

To perform the persistency tests the Detector is initially saturated. It is exposed to the laboratory radiation during 1 minute with no filter placed and then it is covered with a cool blank. A series of images P1, P2, P3 etc is taken as describedP1: Immediately after saturation, 1 reset cycle is made followed by 4 readouts,a 10 minutes wait and other 4 readouts. So P1 is: 1 reset, 4 readouts, 10’, 4 readouts. Following this scheme:P2: 2 resets, 4 readouts, 10’, 4 readoutsP3: 3 resets, 4 readouts, 10’, 4 readouts and so on.As can be seen in the picture the behaviour is different due to the need to repeat the Reset cycle to remove the effect associated to the initial saturation. Also, a dark current increase is associated to the previous saturation of the detector.

Detector response after saturation. Dark current vs saturation

Saturation vs non saturation.

The figure compares the behaviour of two different areas of the detector. The blue graph corresponds to a previously saturated area while the red one has not been saturated before the measurements. As it can be seen the Dark Current is strongly dependent and is a remarkable persistency effect.

Persistency

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Abstract