Semitransparent Amorphous Silicon Strip Sensors

Transcription

1 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

2 Contents! Concept and Motivation! Sensor Design and Performance! New Test Results! Applications Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

3 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

4 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

5 ALMY Sensor Design Active Area No. of Strips Strip pitch Strip width a-si thickness Bias voltage Eff. Band gap 20 x 20 mm 2 64 x µm 300 µm µm 1 V 0.82 ev! < 1 µm thick active layer of hydrogenated amorphous silicon! Transparent strip electrodes! 1 mm thick glass substrate! Photo current < 1 µa/ strip Transmittance at 690 nm at 780 nm Pos. resolution Beam deflection % % < 5 µm < 5+/- 5 µrad Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

6 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

7 Readout Electronics! 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 Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

8 ALMY Sensor Modules Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

9 Amorphous Silicon Strip Photo Diodes Illuminated Schottky diodes p-i-n diodes Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

10 Amorphous Silicon Strip Photo Diodes Dark current Schottky diodes Schottky diodes p-i-n diodes Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

11 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

12 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

13 Transmittance Transmittance 780 nm:! Uniform: antireflective coating of the glass! Optimized sensor layer thicknesses Wavelength 88% Transmittance 690 nm: Transmittance 76% 64% Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

14 Photo Current Response Relative response! Uniformity better than 5%! Absolute sensitivity (for 1 µm thick a-si:h): nm nm! Saturation intensity (1 µa strip current): 100 mw/cm 780 nm 10 mw/cm 690 nm Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

15 Position Resolution and Linearity Resolution of 1 µm achieved over 20 x 20 mm 2 sensor area: x = x meas x stepping motor S/N > 1000 Local resolution «1 µm Typical resolution: 5 µm Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

16 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 O Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

17 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 hours peak illumination with 10 mw/cm 690 nm: Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

18 Long Term Illumination At maximum signal intensity for each wavelength 100 mw/cm 780 nm 10 mw/cm 690 nm 1% aging/500 hours 2.5%/1500 hours % aging/500 hours Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

19 Long Term Illumination 100 mw/cm 780 nm + daylight 3.5% aging/500 hours! 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 Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

20 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 = 10 8 measurements is only +/- 5 µm Hubert Kroha, MPI f. Physik, Munich Beaune, June

21 Radiation Hardness Sensors w/o electronics after neutrons/cm 2 (1MeV): No changes in transmittance, IV characteristics, dark current Dark current IV characteristics Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

22 Radiation Hardness Sensors with electronics after neutrons/cm 2 (1MeV):! < 2% average loss in sensitivity! Electronics and laser diodes survive at least neutrons/cm 2 Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

23 ALMY Sensor Applications! ATLAS muon spectrometer (demonstration that the strictest requirements are fulfilled)! CMS muon detector: 30 x 30 mm 2 sensors under preparation! HERA-B silicon tracker! ZEUS silicon vertex detector (5 x 5 mm 2 sensors produced)! Test of 10 sensors/laser beam in TESLA Test Facility at DESY! Commercial applications ALMY Sensors Laser source Hubert Kroha, MPI f. Physik, Munich Beaune, 19 June

24 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