In this activity, we develop novel focal plane detector pixels for the next generation CMB B mode detection missions. Such future mission designs will require focal plane pixel technologies that optimizes the coupling from telescope optics to the large number of detectors required to reach the sensitivities required to measure the faint CMB polarization traces. As part of an ESA Technical Research Programme (TRP) programme we are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays to reduce the focal plane size requirement. The concept of replacing traditional single channel pixels with multi frequency pixels will be a key driver in future mission design and the ability to couple radiation effectively over larger bandwidths (30 - 100%) is a real technical challenge. In the initial part of the programme we reviewed the science drivers and this determined the technical specifications of the mission. Various options for focal plane architectures were considered and then after a tradeoff study and review of resources available, a pixel demonstrator was selected for design manufacture and test. The chosen design consists of a novel planar mesh lens coupling to various planar antenna configurations with Resonant Cold Electron Bolometer (RCEB) for filtering and detection of the dual frequency signal. The final cryogenic tests are currently underway and a final performance will be verified for this pixel geometry.
novel type of the multichroic “seashell” resonant antenna is developed for CMB measurements. The polarized slot
antennas are arranged in the compact form of a seashell with individual slots for each frequency and each polarization.
Such an arrangement gives unique opportunity for independent adjusting individual parameters of slots with microstrip
lines (MSL) and bolometers. For each frequency band the seashell antenna contains two pairs of orthogonal slots for
each polarization connected by microstrip lines (MSL) with a bolometer in the middle for in-phase operation. To fit slots
in λ/2 area for the best beam shape, lumped capacitances in the form of H-slot were introduced. Ellipticity of a beam was
improved to the level of better than 1%.
The seashell antenna gives a unique opportunity to select needed bandwidth by resonant properties of slots themselves.
Slots are phased by MSLs connecting two opposite slots with a resistive Cold-Electron Bolometer (CEB) placed just in
middle of two MSLs. MSLs and CEBs are placed just in the area of the seashell antenna. The resonant seashell antenna
with CEBs avoids long MSLs bringing signal outside the antenna to large external filters as in the case of sinuous
antenna. This innovation avoids losses in long MSLs and increases frequency range.
The main objective of this activity is to develop new focal plane coupling array concepts and technologies that
optimise the coupling from reflector optics to the large number of detectors for next generation sub millimetre
wave telescopes particularly targeting measurement of the polarization of the cosmic microwave background
(CMB). In this 18 month TRP programme the consortium are tasked with developing, manufacturing and
experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays
which will be demanded to reach the required sensitivity of future CMB polarization missions. One major
development was to have multichroic operation to potentially reduce the required focal plane size of a CMB
mission. After research in the optimum telescope design and definition of requirements based on a stringent
science case review, a number of compact focal plane architecture concepts were investigated before a pixel
demonstrator consisting of a planar mesh lens feeding a backend Resonant Cold Electron Bolometer RCEB for
filtering and detection of the dual frequency signal was planned for manufacture and test. In this demonstrator
the frequencies of the channels was chosen to be 75 and 105 GHz in the w band close to the peak CMB signal.
In the next year the prototype breadboards will be developed to test the beams produced by the manufactured
flat lenses fed by a variety of antenna configurations and the spectral response of the RCEBs will also be
verified.
Future sky surveys in the mm/sub-mm range, like the forthcoming balloon-borne missions LSPE, OLIMPO, SPIDER etc., will need detectors insensitive to cosmic rays (CRs) and with a NEP of the order of 10-17 ¥ 10-18 W/sqrt(Hz). The Cold-Electron Bolometers (CEBs) technology is promising, having the required proper- ties, since the absorber volume is extremely small and the electron system of the absorber is thermally insulated from the phonon system. We have developed an experimental setup to test the optical performance and the CRs insensitivity of CEBs, with the target of integrating them in the OLIMPO and LSPE focal planes.
The Cold-Electron Bolometer (CEB) is a sensitive millimetre-wave detector which is easy to integrate with superconducting
planar circuits. CEB detectors have other important features such as high saturation power and very fast response. We
have fabricated and tested CEB detectors integrated across the slot of a unilateral finline on a silicon substrate. Bolometers
were fabricated using two fabrication methods: e-beam direct-write trilayer technology and an advanced shadow mask
evaporation technique. The CEB performance was tested in a He3 sorption cryostat at a bath temperature of 280mK. DC
I-V curves and temperature responses were measured in a current bias mode, and preliminary measurements of the optical
response were made using an IMPATT diode operating at 110GHz. These tests were conducted by coupling power directly
into the finline chip, without the use of waveguide or feedhorns. For the devices fabricated in standard direct-write technology,
the bolometer dark electrical noise equivalent power is estimated to be about 5×10-16W/√Hz, while the dark
NEP value for the shadow mask evaporation technique devices is estimated to be as low as 3×10-17W/√Hz.
A novel concept of the parallel/series array of Superconducting Cold-Electron Bolometers (SCEB) with a
superconducting absorber and a SIS' (Superconductor-Insulator-Weak Superconductor) Tunnel Junctions has been
proposed. The current-biased SCEBs are connected in series for DC and in parallel for HF signal. A signal is
concentrated to the absorber through the capacitance of tunnel junctions and additional capacitance for coupling of
superconducting islands. Due to dividing power between an array of SCEBs and increasing responsivity, the noise
matching is so effective that the photon NEP could be easily achieved at 300 mK with a room temperature JFET readout.
The concept has been developed for matching with JFET readout for BOOMERanG balloon telescope. BOOMERanG is
devoted for measuring the CMB polarization.
Several technologies are now being considered for modulating the polarization in various B-mode instruments, including rotating quasioptical half-wave plates in front of the focal plane array, rotating waveguide half-wave plates and Faraday rotators. It is not at all clear that any of these techniques is feasible without heavy penalty in cost or performance. A potentially much more efficient method is to use a pseudo-correlation polarimeter in conjunction with a planar circuit phase switch.
We investigate three different devices for use as mm-wave switches, SIS tunnel junctions, capacitively coupled superconducting nanostrips and RF MEMS. The SIS tunnel junction switches operate by switching between two different bias voltages, while the nanostrip switch operates by changing the impedance of a resonant circuit by driving the nanostrip from the superconducting to normal state. In each case the RF signal sees two substantially different complex impedance states, hence could be switched from one transmission line branch to another. In MEMS this is achieved by mechanical movement of one plate of a parallel plate capacitor system. Although RF MEMS have been reported at high microwave and low mm-wave frequencies, in this work we have investigated cryogenic MEMS for operation at high mm-wave frequencies (225 GHz) using superconducting transmission lines.
We present and compare designs and simulations of the performance of phase switches based on all three switching technologies, as well as preliminary experimental results for each of the switches. Finally we also present designs of phase shift circuits that translates the on/off switching into phase modulation.
For sensitive wideband spectroscopy at TeraHertz frequencies one needs a wide-range electrically tunable THz source and a sensitive detector. In this paper a superconducting normal metal cold electron bolometer (CEB) was used as a broadband sensor. Bolometers were integrated with broadband log-periodic antenna designed for 0.2-2 THz frequency range and double-dipole antennas designed for 300 and 600 GHz central frequency. A Josephson junction was used as a wide band electrically tuned terahertz cryogenic oscillator. Bicrystal YBaCuO Josephson junctions demonstrated a characteristic voltage IcRn of over 4 mV that corresponds to characteristic frequency about 2 THz. The bolometer chip is attached to a Si substrate lens at 260 mK and the oscillator chip is attached to the sapphire substrate lens at 1.8 K, with lenses facing each other at the distance of few centimeters. High signal was measured in the whole frequency range up to 1.7 THz by simple changing the bias voltage of Josephson junction from zero to 3.5 mV. A voltage response of the bolometer up to 4*108 V/W corresponds to an amplifier-limited technical noise equivalent power of the bolometer NEP=1.25*10-17 W/Hz1/2. Combining a Terahertz band Josephson junction, a high-sensitive hot electron bolometer, and a sample under test in between, makes it possible to develop a cryogenic compact Terahertz-band transmission spectrometer with a resolution below 1 GHz corresponding to the linewidth of Josephson oscillations. For frequencies below 600 GHz a conventional Nb shunted SIS junction can be used as Josephson oscillator.
A novel concept of the Cold-Electron Bolometer (CEB) with strong electrothermal feedback has been proposed. The concept is based on direct electron cooling of the absorber that serves as negative electrothermal feedback for incoming signal. This feedback is analogous to TES (transition-edge sensor) but additional dc heating is replaced by deep electron cooling to minimum temperature. It could mean a principle breakthrough in realization of supersensitive detectors. Noise properties are considerably improved by decreasing the electron temperature. The loop gain of electrothermal feedback could exceed 1000. The response time is reduced by electrothermal feedback to 10ns in comparison with the intrinsic e-ph time constant of 10ms.
The CEB gives opportunity to increase dynamic range by removing all incoming power from supersensitive absorber to the next stage of readout system (SQUID) with higher dynamic range. Saturation problems are not so severe for CEB as for TES: after exceeding the cooling power there is only slight deviation from linear dependence for voltage response. The full saturation comes at the level of 100pW when temperature of absorber achieves Tc of Al.
Ultimate performance of the CEB is determined by shot noise of the signal readout. For relatively low background load P0 =10fW and quantization level Te= 50mK, the limit NEP is equal to 10-19W/Hz1/2. The estimations show that it is realistic to achieve ultimate NEP at 100 mK with SQUID readout system and NEP=10-18W/Hz1/2 at 300mK for background load of 10fW. Applicability of the CEB to post-Herschel missions looks very promising.
A capacitively coupled hot-electron nanobolometer (CC-HEB) is the simplest and most effective antenna-coupled bolometer. The bolometer consists of a small absorber connected to the superconducting antenna by tunnel junctions. The tunnel junctions used for high-frequency coupling also give perfect thermal isolation of hot electrons in the small volume of the absorber. The same tunnel junctions are used for temperature measurements and electron cooling. This bolometer does not suffer from the frequency limitations in the submillimeter range due to the high potential barrier of the tunnel junctions as does the microbolometer with Andreev mirrors (A-HEB), which is limited by the superconducting gap. Theoretical analyses show that the two-junction configuration more than doubles the sensitivity of the bolometer in current-biased mode compared to the single-junction configuration used for A-HEB.
Another important advantage of CC-HEB is its simple two-layer technology for sample fabrication. Samples were fabricated with an absorber made of a bilayer of Cr and Al to match the impedance of the antenna. Electrodes were made of Al and tunnel junctions were formed over the Al oxide layer. The coupling capacitances of the tunnel junctions, C ≈ 20 fF, in combination with the inductance of the 10 μm absorber create a bandpass filter with a central frequency around 300 GHz. Bolometers are integrated with log-periodic and double-dipole planar antennas made of Au. The temperature response of bolometer structures was measured at temperatures down to 256 mK. In our experiment we observed dV/dT=1.3 mV/K, corresponding to responsivity S=0.2.109 V/W. For amplifier noise Vna=3nV/Hz1/2 at 1 kHz the estimated total noise equivalent power is NEP=1.5.10-17 W/Hz1/2. The intrinsic bolometer self noise Vnbol=0.5 nV/Hz1/2 corresponds to NEP=3.10-18 W/Hz1/2. For microwave evaluation of bolometer sensitivity we used a black body radiation source comprising a thin NiCr stimulator placed on the cold plate of cryostat in front of a CC-HEB attached to an extended hemisphere sapphire lens. This measurements were consistent with estimates based on the dc responsivity of the bolometer.
The current-voltage characteristics of a superconductor-normal metal tunnel junction (SIN) is very sensitive to the temperature of the normal metal. Therefore SIN junction can be used as a thermometer which can be conveniently integrated into more complicated devices, for example bolometers. We estimate the effect of different types of noise on the sensitivity of such a thermometer. Shot noise of the tunnel junction, amplifier noise and the noise related to the fluctuations of the heat flow through the junction are considered. The performance of the bolometer with SIN junction as a temperature sensor is also discussed.
We present the results of experimental development of an ultrasensitive normal metal hot-electron microbolometer with Andreev mirrors and electronic cooling by superconductor- insulator-normal metal (SIN) tunnel junctions. A value NEP equals 5 (DOT) 10-18 W/Hz1/2 for the temperature fluctuations component of noise and the thermal time constant (tau) equals 0.2 microseconds at 300 mK have been estimated for one of the realized devices with thermal conductance G approximately equals 6 (DOT) 10-12 W/K. At 100 mK, the thermal conductance was decreased to G approximately equals 7 (DOT) 10-14 W/K, that gives NEP equals 2 (DOT) 10-19 W/Hz1/2 for the temperature noise component and a thermal time constant (tau) equals 5 microseconds. Such microbolometer is intended as a detector of millimeter and submillimeter wave radiation for space applications.
A novel concept of the hot-electron bolometer using a microrefrigeration by SIN tunnel junctions for direct cooling the electrons of the absorber has been proposed. We have analyzed the most attractive case of cooling starting from 300 mK that can be achieved in a simple cryostat with 3He pumping. Electronic cooling to 50 - 100 mK has shown considerable decrease of the electron-phonon thermal conductance Ge-ph but small decrease of G(Sigma ) equals Ge-ph + Gcool in comparison with Ge-ph before cooling. The maximum decrease of GSigma by a factor of 1.8 has been achieved at temperatures around 200 mK. The analysis shows that the noise equivalent power (NEP) can be decreased using direct electronic cooling. The thermal noise component of NEP is decreased by a factor of 3 for electronic cooling from 300 to 100 mK mainly due to decrease of the electron temperature (and small decrease of G(Sigma )). Tunnel junction noise and amplifier noise components of NEP can also be improved by a factor of 4 due to increase of the power responsivity. For general noise analysis we used analytical expressions for main noise components and I-V curve of SIN tunnel junctions. The optimal bias currents were found for short noise component and amplifier noise component.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.