Semitransparent Amorphous Silicon Strip Sensors F.Bauer, V.Danielyan, S.Horvat, H.Kroha Max-Planck-Institut für Physik, Munich

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

1

Contents Concept and Motivation ! Sensor Design and Performance ! New Test Results ! Applications !

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

2

Motivation

!

! ! !

Optical alignment monitoring system for the ATLAS Muon Spectrometer and Inner Tracker: ALMY Sensors Misalignment corrections on muon sagitta to 30 µm (rms) Sensor position resolution < 5 µm over > 1 cm meas. range (2D) Several 100 sensors and laser beams, radiation hard Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

3

Laser Beams !

!

!

!

!

Multipoint alignment system Position and angle measurements Laser diodes coupled to single mode fibers Collimated laser beams with gaussian profile Wavelengths: 690 nm and 780 nm (visible)

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

4

ALMY Sensor Design

!

! ! !

< 1 µm thick active layer of hydrogenated amorphous silicon Transparent strip electrodes 1 mm thick glass substrate Photo current < 1 µA/ strip Hubert Kroha, MPI f. Physik, Munich

Active Area

20 x 20 mm2

No. of Strips

64 x 64

Strip pitch

312 µm

Strip width

300 µm

a-Si thickness

0.3-1.0 µm

Bias voltage

1V

Eff. Band gap

0.82 eV

Transmittance at 690 nm

70-75 %

at 780 nm

80-90 %

Pos. resolution

< 5 µm

Beam deflection

< 5+/- 5 µrad

Beaune, 19 June 2002

5

Transparent Photosensors !

Thin layers of amorphous silicon are transparent for visible light, especially at 690 nm and 780 nm (available as laser diodes)

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

6

Readout Electronics

! !

!

! !

Hubert Kroha, MPI f. Physik, Munich

RS232 interface for single sensor RS485 interface for up to 30 sensors on PC serial port CANBus interface under development Integrated laser controller Measurement time 20 ms

Beaune, 19 June 2002

7

ALMY Sensor Modules

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

8

Amorphous Silicon Strip Photo Diodes Illuminated

p-i-n diodes Schottky diodes

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

9

Amorphous Silicon Strip Photo Diodes Dark current

Schottky diodes

Schottky diodes

p-i-n diodes

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

10

Sensor Qualification

About 100 Sensors tested Position Measurement

Scan of sensor with laser beam: 1) Transmittance, uniformity 2) Position measurement 3) Laser beam deflection angle Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

11

Sensor Uniformity Transmittance

Interference patterns in transmittance and absorption, distortion of laser beam profile: !

!

If wedge angle between glass surfaces Without antireflective coating of the back side of the glass substrate

Use lasers with short coherence length. Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

12

Transmittance !

!

Transmittance 80-90% @ 780 nm:

Uniform: antireflective coating of the glass Optimized sensor layer thicknesses Wavelength

Transmittance

88%

Transmittance 70-75% @ 690 nm:

76%

64%

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

13

Photo Current Response Relative response

!

!

!

Hubert Kroha, MPI f. Physik, Munich

Uniformity better than 5% Absolute sensitivity (for 1 µm thick a-Si:H): 0.01 A/W @ 780 nm 0.1 A/W @ 690 nm Saturation intensity (1 µA strip current): 100 mW/cm2 @ 780 nm 10 mW/cm2 @ 690 nm

Beaune, 19 June 2002

14

Position Resolution and Linearity Resolution of 1 µm achieved over 20 x 20 mm2 sensor area:

x = xmeas – xstepping motor S/N > 1000 Local resolution « 1 µm

Typical resolution: 5 µm

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 19June June2002 2002

15

Laser Beam Deflection !

!

!

!

Specially polished glass wafers with parallel surfaces No deformations during coating and sensor prod. Deflection angles < (5 +/– 5) µrad Includes beam distortion due to interference effects Hubert Kroha, MPI f. Physik, Munich

O

Beaune, 19 June 2002

16

Long Term Illumination !

!

Degradation of the light sensitivity of a-Si:H under illumination ( Staebler, Wronski 1977, solar cells) Observation of the effect localized at the laser spot, e.g. 1500 hours peak illumination with 10 mW/cm2 @ 690 nm:

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

17

Long Term Illumination 100 mW/cm2 @ 780 nm

At maximum signal intensity for each wavelength 10 mW/cm2 @ 690 nm

1.5-2.5% aging/500 hours 1% aging/500 hours 2.5%/1500 hours

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

18

Long Term Illumination mW/cm2 @

100 + daylight

!

780 nm !

!

3.5% aging/500 hours

Hubert Kroha, MPI f. Physik, Munich

Add. uniform daylight exposure corresp. to saturation current Aging rate at laser spot relative to rest of sensor surface, effect not additive Non-linear increase of aging rate with illum. intensity

Beaune, 19 June 2002

19

Long Term Illumination !

!

!

!

Degradation rate increases with the illumination intensity, as predicted by models (solar cells) Because of the observed wavelength dependence it increases with the absorbed light intensity ALMY sensor degradation rate is small and constant at the small operating laser intensities for which the readout electronics is optimized Absolute local position meas. error after 500 hours cont. illumination = 108 measurements is only +/- 5 µm

Hubert Kroha, MPI f. Physik, Munich

Beaune,19 19June June2002 2002 Beaune,

20

Radiation Hardness Sensors w/o electronics after 1014 neutrons/cm2 (1MeV): No changes in transmittance, IV characteristics, dark current

Dark current

IV characteristics Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

21

Radiation Hardness Sensors with electronics after 1013 neutrons/cm2 (1MeV): !

!

< 2% average loss in sensitivity Electronics and laser diodes survive at least 1013 neutrons/cm2

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

22

ALMY Sensor Applications !

!

! !

!

!

ATLAS muon spectrometer (demonstration that the strictest requirements are fulfilled) CMS muon detector: 30 x 30 mm2 sensors under preparation HERA-B silicon tracker ZEUS silicon vertex detector (5 x 5 mm2 sensors produced) Test of 10 sensors/laser beam in TESLA Test Facility at DESY Commercial applications

Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

ALMY Sensors

Laser source

23

Conclusions !

! ! !

!

Development of novel transparent optical position sensors (ALMY) Optimization of performance Flexible, compact readout electronics Applications in optical alignment monitoring systems of HEP experiments Preparation of larger-scale sensor production in progress Hubert Kroha, MPI f. Physik, Munich

Beaune, 19 June 2002

24