IWORID 2006, July 4 th 2006

Transcription

1 An integrated single photon detector array using porous anodic alumina Joost Melai, Cora Salm, Jurriaan Schmitz, Sander Smits, Jan Visschers IWORID 2006, July 4 th IWORID Joost Melai 1

2 Overview Goal: A prototype single photon detector array manufactured monolithically on an imaging ASIC like Medipix2 Idea and motivation Requirements of the MCP First experimental results Conclusions and outlook IWORID Joost Melai 2

3 The idea e multiplication in an MCP Detector system: Photo-Cathode Electron multiplication structure Medipix imaging ASIC photon e photocathode vacuum E pixels electronics Medipix IWORID Joost Melai 3

4 Existing Knowledge Belarus academy of science + Samsung Research: Alumina MCPs Anodic alumina made in MESA+ (Univ. Twente) Vallerga et al. (UC Berkeley): Medipix + discrete MCP + photo-cathode IWORID Joost Melai 4

5 The porous alumina MCP detector cathode porous Al2O3 anode wafer with pixel pads Using micro-electronics technology: other geometries structural integrity (substrate) different materials different voltages? IWORID Joost Melai 5

6 Gain Geometry Requirements I 500 V 1000 V 1500 V 2000 V Saturation at gain-diameter ratio of around /m Lower limit: 10 nm No Nano-Channel Plate MCP with G > 1000 d > 0.1 µm and α > 50 L > 5 µm aspect ratio Gain limit: α > 50 Technology: α lower Standard models by Wiza (NIM 79) and Eberhardt (Appl Opt. 79) IWORID Joost Melai 6

7 Geometry Requirements II Varying aspect ratio (α) Gain α = 100 α = 70 α = 60 α = 50 Dielectric strength limits voltage V [V] SiO 2 Si 3 N 4 Al 2 O α = α = V [V] 1000 Ta 2 O 5 0 TiO L (µm) Standard models by Wiza (NIM 79) and Eberhardt (Appl Opt. 79) IWORID Joost Melai 7

8 Discrete porous alumina disks Available from Whatman for fluid filtration, 60 µm thick, 0.2 µm pores IWORID Joost Melai 8

9 Metallization of alumina disk 10 nm Au/Pd Pores still open Au penetration around 0.2 µm IWORID Joost Melai 9

10 Measurements on alumina disks Metal contacts defined Capacitance-Voltage measurements prove functionality Investigation of bias capability Functional measurement on dimpled disks porous Al 2 O kv I out HV A vacuum I in IWORID Joost Melai 10

11 Bias curve for alumina disks 6.E-05 5.E-05 J [A/cm2] 4.E-05 3.E-05 2.E-05 1.E-05 0.E V [V] Some samples are clearly more leaky than others Current densities not excessive Area of Medipix2 pixel (55 55 µm 2 ) current < 0.6 na IWORID Joost Melai 11

12 Porous Al 2 O 3 made by anodization Pt A wafer with Al 500 pore distance [nm] 250 acid 2 Al + 3 H 2 O Al 2 O 3 + 3H Anodization voltage [V] A.P. Li et al., (MPI Halle), J. Appl. Phys wt% Phosphoric acid ~ V 200 nm IWORID Joost Melai 12

13 Integration challenge remaining Al Anodization into bond-pads Incomplete anodization growing oxide Al bond pad sub-electrode Sub-electrode acts as stopping layer Sub-electrode shorts all pixels No photo-lithography IWORID Joost Melai 13

14 1 2 3 pixel 1 pixel 2 Ni on TiW thick Al Compound sub-electrode Etch Ni selective to TiW with HCl or HNO 3 4 Porous Anodic Alumina Ni and TiW both act as counter-electrode 5 Photo- Cathode Etch TiW selective to Ni with F plasma (dry) or H 2 O 2 (wet) IWORID Joost Melai 14

15 Conclusions Integrated MCP based on porous alumina Promising experiments on discrete disks Functional metallization Reverse bias > 1500 V, limited leakage First anodization experiment successful Integration scheme for wafer-scale post-processing IWORID Joost Melai 15

16 Acknowledgements: Victor Blanco Carballo Max Chefdeville Harry van der Graaf STW