1. One of the activities of the spatial team of the CNRS/CRTBT Samuel Leclercq, CNRS/CRTBT (Grenoble, France) European Network on Applied Cryodetectors Munich, Germany, 7th November 2003

2. Projects Bolometric Camera for Millimetre wavelengths Diabolo Archeops Planck Edelweiss II Team Alain Benoit Philippe Camus François-Xavier Désert Samuel Leclercq One of the activities of the spatial team of the CNRS/CRTBT

3. Goals for the bolometric camera 64x64 pixels @ =1.2 mm (250 GHz), 1.5x1.5 mm 2 /pixel (FWHM 8.5") 32x32 pixels @ =2.1 mm (143 GHz), 2.6x2.6 mm 2 /pixel (FWHM 15")  Shannon sampling of the unvignetted 260" field of view at the IRAM 30m telescope.  1 hour for the detection of a 3mJy source (F galaxy ≈ 10 12 L  ) (10 hours with best actual instruments) Reach optimum abilities of the IRAM 30 m telescope : angular resolution and photon noise. SZ effect and high z galaxy mapping. For one pixel with 1 mm water vapour in atmosphere, and instrument NEP = 50% of total photon NEP : 1 Jy = 10 -26 W/m 2 /Hz

4. Exemple of electro- thermal tests. 80mK 150mK 200mK 300mK NbSi single bolometer Bolometer on thin Si 3 N 4 membrane L=300  m S=60  m 2 NbSi : Anderson insulator, variable range hopping. Goal : reach the metal-insulator transition at the dilution temperature (100 mK). Efros and Shklovskii law : NbSi Au/Cr Au/Cr (thermal link) Bi (absorber) NEP : 5.10 -17 W/ Optimisation : A ≈ 10 and R fit to the electronic read out.  Controlled by the shape of the NbSi thin layer + Nb composition 

5. #1 à #8 #10 #13 #11 Lithography : <0 resist and 365nm UV exposure Au ≈ 1500 Å Ti ≈ 50 ÅNb ≈ 500 Å Ir ≈ 50 Å NbSi ≈ 1000 Å SiO ≈ 250 Å Only wafers #11 and #13 have Nb electrodes deposited with mechanical mask. 4 kinds of arrays tested Resist / Lithography Shadow mask NbSi arrays Smooth edges  no contact problems No resist  no pollution problems

6. Fits : R 0 = 1,1 k  16 < T 0 (K) < 18,8 R(V) = V/I still too high at low V. Films not as homogenous as expected. Yet, shapes fits with electron-phonon decoupling : g e–ph = 100 W/K 5 /cm 3. Better results on #13 (data processing in progress). NbSi arrays Tests on wafer #11

7. Electronic multiplexing Necessity for a cold multiplexing system with low current and low noise electronic Without multiplexing system Matrix NxN  N 2 +2 wires between dilution and 300K  too much. Ex matrix 32x32  1026 wires. input polarisation NxN output signals bolometer matrix only R load R bolo Matrix NxN  2N+2 wires. Advantages : volume occupied and conductive heat loads by wires, dissipation from cold JFET amplifiers. Ex matrix 32x32  66 wires. With multiplexing system Commutation transistor : HEMTs Capacity filtering transient effects : C  1 nF bolometer and transistors matrixes N commutation lines N output signals

8. Electronic time multiplexing for high Z LTD FREQUENCY REQUIREMENTS  Bolometer Signal bandwidthB = 10 Hz  Bolometer Sampling frequencyF sampling > 2 B ELECTRICAL NOISE ANALYSIS  Bolo Johnson noise e N,bolo = (W/ )  Read time/pixel t mes = 1/F samping  Amplifier HF noise e N,ampl (W/ )  Sample RMS noise TYPICAL DESIGN Rb = 10M  ; C INT = 1.6 nF ; T=100mK ; e N,bolo =7.4 nV/ CAPACITIVE POLARISATION No power dissipation at low temperature Cold capacity (C POL ~ 5pF) to avoid any leakage current Minimisation of transient effects when commutation occurs

9. In progress : conception and test of a complete bolometer matrix with bow tie absorber antennas 1) nitruration 2) RIE (SF 6 ) 3) KOH  thermal membrane 4) Nb electrodes with shadow mask 5) NbSi thermometer with shadow mask 6) Au track lithography 7) SiO 2 isolation 8) Nb antennas lithography 9) Bi shunt lithography 10) KOH opening membranes

10. In progress : conception and test of a complete bolometer matrix with bow tie absorber antennas Test of antennas absorption on a Fourier Transform Interferometer (Martin Pupplet)

11. Very low capacity Cgs~1fF R ON 10 7  Array of 13 HEMTs with common source in PLCC-28 supports Ig<0.1pA Small voltage variation for switching Conduction noise = Johnson [PRL] In progress : development of Quantum Point Contacts HEMTs too improve the multiplexing system

12. Coming next NbSi : - Electric tests on a bolometer matrix  with field effect and electron-phonon decoupling fittings. - Fourier Transform on V(I) curves  Phonon, Johnson, 1/F and "pop corn" noises. Antennas : - Numerical analysis of electromagnetic absorption by antennas with a fourth wave cavity (in progress). - Conception of a Martin Pupplet interferometer. - Studies on different shapes and tests with the Martin Pupplet. Bolometers : - Finishing the electronic and instrument control program. - Heat transfers in membranes. - Photon noise recording and calibration with a black body (in progress) Around the matrix : - radiation filters - dilution fridge for the camera - lenses and mirrors for adaptation on the IRAM 30 m telescope Optical axe of the telescope (F/D=10) Field mirror Focal plane of the field mirror on the cold lens Image of the sky < 1 m