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Cryogenic Electronics for Space Applications and Research

Final Report Summary - CESAR (Cryogenic Electronics for Space Applications and Research)

Executive Summary:
In the coming decade, the European Space Agency has scheduled programs in X-ray and far infrared astronomy with improved cryogenic detector arrays (number of pixels and signal sensitivity). Nevertheless these developments are slowed down by the restricted amount of available power, at low temperature, in space conditions. The power budget is mainly consumed by the ever-growing number of wires that link the cooled detectors to the distant (∼10 m) warm electronics. A possible solution is the development of the signal processing functions at the heart, or close to the detectors themselves. The development of such cryogenic and complex electronics is the goal of CESAR. The three steps are presented below: cryogenic front-end electronics with intrinsic properties as good as the detector ones, complex electronics circuits (amplifiers, filters, multiplexers, DACs and ADCs) working at or below 4 K, and combination of both developments and end-to-end tests on large 2D arrays (multiplexed X-ray microcalorimeters, far-infrared bolometers and magnetometers). One of the CESAR peculiarities is this three level complementarity and dependence between the different technical work packages: components/circuits/physical applications.
The objectives have been fulfilled: we are now able to measure cryogenic electronic devices manufactured during the CESAR process, not only at the elementary component level, but also at the circuit level. All the measurements are not positive. Many reasons for that: Nature at the fundamental level is most of the time different from the way we think it. The logical consequence is that experiments are not supposed to work, except when you develop a step-to-step strategy to overcome all the possibilities to fail. Sometimes a surprise can occur. In science we call that serendipity. This was the case during the GeJFET development. It is not yet guaranteed that we can produce this kind of component in a well-defined and reproducible process, but the way to realize “clean” electrical contacts in Ge or other transistor types is now straightforward. The very high doping level contact obtained by laser pulses is now well established.
The quest for HEMTs with very high noise quality working at very low temperature was a long quest in many labs around the world. Thanks to the CESAR program, due to the internal visibility given by this type of European Grant at the institutional level, the program could be achieved. These HEMTs were later incorporated to more fields of the CESAR development (Magnetometry) than initially planned. The LPN HEMTs were, outside the CESAR program, widely distributed in most of the preeminent Dark matter experiments (CDMS, EDELWEISS,…).
At the semi complex level, the CMOS ADC chips gave excellent results very soon in the CESAR development. Some failures on other chips have the manufacture of complex circuits. This gave time to built and test efficiently the setup for the defined applications: X-Ray Calorimetry, Far Infrared Photometry and space magnetometry.
Project Context and Objectives:
Observations from space are now one of the main activities of the space agencies and space industries around the world. The observed electromagnetic spectral range is expanding to high-energy photons: X and gamma rays in one direction, and to very low energy photons between far InfraRed and millimeter wavelength in the other. For technical reasons, in both domains, the current imaging quality (number of pixels), spectral resolution and sensitivity are insufficient to the scientific needs. In addition the totality of the X and gamma ray and most of the FIR to millimeter domain can only be observed from space, because strong atmospheric opacity in these wavelengths. To get a huge improvement in spectral resolution and sensitivity the use of cryogenic sub-kelvin detectors is mandatory. On the detector side, the technological step has already been done with new devices. The development of large (many pixels) focal plane arrays is restricted by a necessary tradeoff between the limited amount of cryogenic power/energy available in space conditions, and the thermal load induced by the number of shielded wires needed to transport the high impedance signals from the cold stage up to the sophisticated warm electronics in the service module. Nevertheless, current developments in cryogenics show that in a near future, complete autonomous and long operating solutions will be available to cool down detectors at 50 mK without the need to launch large cryostats filled with 1000’s liters of liquid helium.
The only way to overcome this apparent contradiction is the development of front and back end electronics as close as possible to the detectors to preserve the signal integrity from transport degradation. Ideally, the solution would be to perform all the signal processing – impedance adaptation – amplification – filtering - multiplexing and even digitalization at the cold stage.
In parallel to electromagnetic detection, magnetometers are one of the most common and critical in-situ payload instruments and are included as key payload on a number of ESA Cosmic Vision candidate missions (Solar Orbiter, JUICE). Current space magnetometer technology is primarily dominated by mass heavy fluxgate sensors, which are large volume, high power and require dedicated heaters. Newly developed GMR sensors feature much lower mass and volume and have very high performance at cryogenic temperature. Cold and reliable electronics would help strongly to the development of such ultra sensitive magnetometers.


The goal of CESAR is to develop a high performance cryogenic electronics and demonstrate its efficiency through three applications in the space research domain.

1) To develop a cryogenic FRONT END electronics
The aim is to develop low temperature single devices, beyond current silicon JFETs, made in other materials than pure silicon, working below 4K with very low noise level. Their noise properties will be determined by the sensor quality.
Mainly three types of components are investigated: AsGa, Ge and SiGe based transistors.

2) To develop a BACK END cryogenics electronics
The aim is to develop complex circuits with sophisticated functions, like low noise 2-4 K Operational Amplifiers (SiGe) and CMOS Analog-to-Digital or Digital-to-Analog converters (8-12 bits at 10 kHz, <30K) and CMOS switched buffers and multiplexers at 300 mK.
3) To incorporate high performance cryogenic electronics in three applications.
The aim is to demonstrate the performances of the developed electronics in objective 1 and 2 for three pioneering applications:
- a 2D X-ray microcalorimeter array,
- a 2D far infrared array and
- a 3 axis magnetometer.
Dissemination : To create a European laboratory network in cryogenic electronics.
One main goal of this project is the creation of a European laboratory network in cryogenic electronics development including solid-state physics component researchers and fundamental electronics developers. The results of work done in common could be used with any type of cryogenic application using standard electronic functions in the perspective of high (many pixels) integration either in very low noise acquisition for space applications but also in medical or security applications and magnetometry.

Project Results:
Please read the attached document for more details and figures.

We are now at the end of the CESAR_SPACE Project. All the work done in this framework is meaningless if we cannot put it in the prospective of new developments. New developments can be as well direct applications to space instruments, or follow on of the different themes developed in CESAR, or even new developments made possible by the products of our Project. It is time now to look forward and replace this work in a prospective for future applications.

Single elements.
During the last “Astronomy and instrumentation” SPIE Conference, in June 2014, the importance for Cosmological Microwave Background (CMB) Experiments of the first readout stage became obvious when dealing with thousands of detectors. The faraway Si JFETs are no longer compatible with the experimental setup. Transistors must be located as close as possible of the detector arrays, at kelvin or sub-kelvin temperature. The polarization measurement level required by the detection limits is hampered by the noise (mainly the 1/f side) of the HEMTs manufactured overseas.
The HEMTs developed by CNRS/LPN are already advertised for Dark matter search, and were delivered to the CDMS (US) and Edelweiss (Fr) experiments. We expect these applications (independent from CESAR) will demonstrate to a wider scientific community their intrinsic qualities.
GeJFETs is a grail for more than 20 years in cryogenic electronics. A new manufacturing process is tested in the CESAR Project context. We have not succeeded yet, but very interesting by-products (GUILD contacts) are already used in the microelectronics manufacture platform at CNRS/IEF.

Complex circuits.
The complex circuits developed in the different CESAR applications (X-Ray micro-calorimeter, Far Infrared bolometer arrays and Vector Magnetometry), for readout and signal processing at the cold stage, can have direct applications for future spaces projects.
ATHENA(+) is the second large program of ESA in the 2020’s. The cold circuits developed by CEA/SEDI for X ray Calorimeters can solve many system issues related to the global sensitivity requirements. This is still very dependent of the type of sensors used for the final detectors.

Beyond the Far IR field, the cryogenic circuit developed in the Project can advantageously be used in space for B_MODES detection in the CMB. This topic had recently received a large echo in the Press. Are gravitational waves imprinted in the CMB polarization picture? The detection by BICEP2 at the South Pole observatory is today widely debated. We are confident that a new observatory will be selected either by NASA after the success of WMAP or by ESA after Planck remarkable scientific return. The kind of electronics we have built, in the CESAR context, will be considered at a very general level, because risks on signal degradation can be avoided. This also widely reduces some high level system constraints at the cost of a more sophisticated cryogenic system.

The application to magnetic measurements for planetology is a very interesting case. Despite the ultimate sensor exists for many years now: the Superconducting Quantum Interference Device, its use as an array or in space conditions is not straightforward either because it must be maintained at ~4 kelvins or because the very low impedance of the sensor itself. A good compromise is the Giant Magnetoresistance devices. It can be operated at warmer temperatures, it is a resistive sensor (well adapted to usual electronic circuits), and approaches performance requirements sufficient for many space applications. The CESAR developments show that the association GMR plus cryo-electronics pushes the performance of a 3D device (vector) at an unprecedented sensitivity level for this type of sensor.

Potential Impact:
Please see attached document.
List of Websites:
http://www.cesar-space.eu/

Contacts :
Louis Rodriguez, louis.rodriguez@cea.fr
Vincent Revéret, vincent.reveret@cea.fr

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