Superconducting electron gun for CW operation of superconducting linacs
Electrical characterization of a superconducting hot spot microbolometer
description
Transcript of Electrical characterization of a superconducting hot spot microbolometer
Electrical Electrical characterization of characterization of a superconducting a superconducting
hot spot hot spot microbolometermicrobolometer
S.CibellaS.Cibella, R. Leoni, G. Torrioli, , R. Leoni, G. Torrioli,
M. G. Castellano, A. Coppa, F. MattioliM. G. Castellano, A. Coppa, F. Mattioli
IFN-CNR, Roma, IFN-CNR, Roma, ItalyItaly
Outline Outline THz technologyTHz technology Antenna-coupled superconducting Antenna-coupled superconducting
microbolometers microbolometers Basic principlesBasic principles
Detector fabricationDetector fabrication Electronic readoutElectronic readout I-V characteristic measurementsI-V characteristic measurements NEP measurementsNEP measurements ConclusionsConclusions
THz technologyTHz technologyX Ray Ultraviol
etVisible
Infrared THz gapMicrowave
(millimeter to RF)
1016
Hz 1015
Hz 1014
Hz 1013
Hz 1012
Hz 1011
Hz 1010
Hz1016
Hz1016
Hz
THz frequency domain
1mm (300 GHz) – 100 μm (3 THz)
THz radiation is a potentially powerful technique THz radiation is a potentially powerful technique in security screening applicationin security screening application : :
Penetration Penetration High-resolution 3-D imagingHigh-resolution 3-D imaging SpectroscopySpectroscopy SafeSafe
Antenna-coupled Antenna-coupled superconducting superconducting
microbolometers: how do microbolometers: how do they work?they work? Lithographic antenna electrically coupled to a temperature Lithographic antenna electrically coupled to a temperature
sensor, the bolometer (suspended Nb bridge).sensor, the bolometer (suspended Nb bridge).
N
LH
Antenna
L
TC
Input power modulates Input power modulates the the
current trough the bridge
Modulation of R
Formation of a Normal-state hot spot in the Formation of a Normal-state hot spot in the middle of the suspended superconducting bridge middle of the suspended superconducting bridge per T>TCper T>TC
Modulation the volume of the hot spotModulation the volume of the hot spot
Microbolometer fabricationMicrobolometer fabrication
•100kV FEG•beam spot: 8 nm•Mask fabrication (up to 5”)•direct writing (up to 5”)
3 step process which use electron beam 3 step process which use electron beam lithography (EBL)lithography (EBL)
reactive ions etching (RIE) in CHF 3 /SF6 gas mixture
inductive coupled plasma (ICP) etching in an SF6/Ar gas
mixture
Detector fabricationDetector fabricationSi substrate
100 nm Si3N440 nm Nb
First fabrication step:
•exposure by EBL
• deposition of a 70 nm Ti/Au and lift off to define pads, antennas and alignment markers
Second fabrication step:
•Define the temperature sensor on the HSQ electronic resist
• etching with reactive ions (RIE) in CHF 3 /SF6
gas mixtureNb/Si3N4 bridge
Third fabrication step:
•Expose another HSQ strip layer , 3 um wide, to encapsulate the Nb strip
•Etching by ICP (inductive coupled plasma).
HSQ strip
Bolometer technologies: Bolometer technologies: detector fabrication detector fabrication
Logarithmic spiral antenna with a nominal band from 300 GHz to 1 THz
22x1x0.040 (μm)3
suspended Nb
bridge
Electronic ReadoutElectronic Readout A current sensitive transimpedance amplifier provides:A current sensitive transimpedance amplifier provides: a constant Voltage biasa constant Voltage bias an output related to the bolometer currentan output related to the bolometer current
out b
fb
V VI
R
Bolometer
Rfb=1kΩTo≈5
K
4He
Vacuum can
Rfb
Vout
ZVb
-
+
AD797
Cx=100nF
Rx=1Ω
Cx
Rx I
I-V characteristics I-V characteristics
0 0( )n CV GR T T
0 0
0n
V V VI
R V V
G T
V
VI
R
V0
I
V
0CVI G T T
Linear part: ohmic behavior of the bridge in its normal state
V0
Measured I-V Measured I-V characteristics characteristics
124 /G nW K 24 15B bath
fWNEPph k T G
Hz 78.7nR 0 5.14V mV
Current responsivity (Current responsivity (SSII))
dVZ
dI
1
2I
Z RS
V Z
/R V I
I
IS
P
Measured electrical NEPMeasured electrical NEPRfb
Vb
-
+
40
3.8
NEP fW Hz
V mV
NEP=in
T/SI 2
2 204A
T A nn n
eq eq
kTi i
Z Z
AD 797
in=2 pA/√Hz
Vn=0.9 nV/√Hz
√(NEPPh)2+(int/SI)2
ConclusionsConclusions An antenna coupled hot spot microbolometer An antenna coupled hot spot microbolometer
has been fabricated has been fabricated
A simple room-temperature readout based on a A simple room-temperature readout based on a transimpedance amplifier has been developed transimpedance amplifier has been developed
Noise equivalent power of 40 fW/HzNoise equivalent power of 40 fW/Hz1/21/2 has has been measuredbeen measured
Hot spot microbolometers are a good choice Hot spot microbolometers are a good choice for a THz-camera with a simplified electronic for a THz-camera with a simplified electronic readoutreadout