Ybe Creten

Low-noise low-power readout electronics circuit development in standard CMOS technology for 4 K applications

In the framework of the Photodetector Array Camera and Spectrometer (PACS) project IMEC designed the Cold Readout Electronics (CRE) for the Ge:Ga far-infrared detector array. Key specifications for this circuit were high linearity, low power consumption and low noise at an operating temperature of 4.2K. We have implemented this circuit in a standard CMOS technology which guarantees high yield and uniformity, and design portability. A drawback of this approach is the anomalous behavior of CMOS transistors at temperatures below 30-40K. These cryogenic phenomena disturb the normal functionality of commonly used circuits. We were able to overcome these problems and developed a library of digital and analog building blocks based on the modeling of cryogenic behavior, and on adapted design and layout techniques. We will present the design of the 18 channel CRE circuit, its interface with the Ge:Ga sensor, and its electrical performance. We will show how the library that was developed for PACS served as a baseline for the designs used in the Darwin-far-infrared detector array, where a cryogenic 180 channel, 30μm pitch, Readout Integrated Circuit (ROIC) for flip-chip integration was developed. Other designs and topologies for low noise and low power applications will be equally presented.

Development of a far-infrared Ge:Ga monolithic array for a possible application to SPICA

We present the current status of the development of a far-infrared monolithic Ge:Ga photoconductor array proposed for the SAFARI instrument onboard SPICA, which is a future infrared space mission. SPICA has a large (3-m class) cooled (<6 K) telescope, which enables us to make astronomical observations with high spatial resolution and unprecedented sensitivity in the mid- and far-infrared wavelength. As a candidate detector to cover the 45-110 μm band of a far-infrared focal plan instrument of SAFARI, we are developing a large format monolithic Ge:Ga array. The monolithic Ge:Ga array is directly connected to cryogenic readout electronics (CRE) using the Au-Indium bumping technology. Our goal is to develop a 64×64 Ge:Ga array, on the basis of existing technologies and experience in making the 3×20 Ge:Ga monolithic arrays for the AKARI satellite. In order to realize a larger format array with better sensitivity than that of the AKARI array, we have been making some technical improvements; (1) development of the Au-In bumping technology to realize the large format array, (2) optimization of the structure of the transparent electrode to achieve the better sensitivity, (3) development of an anti-reflection coating to reduce interference fringe between the Ge substrate, and (4) Use of the low-noise cryogenic readout electronics with low power consumption. We fabricated the prototype 5×5 Ge:Ga arrays to demonstrate and evaluate the properties of monolithic array. We demonstrate experimentally the feasibility of these elemental technologies, and also show the results of performance measurements for the prototype Ge:Ga arrays.

Qualification status of the stressed photoconductor arrays for the PACS instrument aboard Herschel

The photoconductor detector arrays for the PACS instrument (Photoconductor Array Camera and Spectrometer) aboard the future ESA telescope Herschel have been developed during the engineering phase in 1999. In early 2000 the construction of the qualification models began for both, the highly and low stressed Ge:Ga arrays, which consist of 12 linear modules each. These two types of photoconductor arrays are dedicated for different wavelengths bands in the spectrometer section of the instrument. While the performance of a few engineering arrays has been studied and presented earlier, additional data are meanwhile available on the absolute responsivity and quantum efficiency of the detectors. Furthermore, experience has been obtained during manufacture of a larger series of arrays giving better statistics on performance aspects, such as uniformity of the cutoff wavelengths and of the responsivity or the maximum stress obtainable within such arrays. Considerable progress has also been made in the development and manufacture of the 4 Kelvin Cold Read-out Electronics (CRE), which will integrate and multiplex the signals generated in each linear array with its 16 detector pixels. Manufacture of the detector arrays for the qualification model is scheduled to be completed by this summer, and manufacture of the flight model has already started. The qualification model will be delivered to the test facilities, where absolute spectral performance of the 24 linear modules will be determined. In this paper we give a summary of the related activities and results as obtained during manufacturing and testing.

A low-noise low-power readout electronics circuit at 4 K in standard CMOS technology for PACS/Herschel

IMEC has designed, in the framework of the PACS project (for the European Herschel Space Observatory) the Cold Readout Electronics (CRE) for the Ge:Ga far-infrared detector array. Key specifications for the CRE were high linearity (3 %), low power consumption (80 μW for an 18 channel array), and very low noise (200 e-) at an operating temperature of 4.2 K (LHT - Liquid Helium Temperature). IMEC has implemented this circuit in a standard CMOS technology (AMIS 0.7 μm), which guarantees high production yield and uniformity, relatively easy availability of the technology and portability of the design. However, the drawback of this approach is the anomalous behavior of CMOS transistors at temperatures below 30-40K, known as kink and hysteresis effects and under certain conditions the presence of excess noise. These cryogenic phenomena disturb the normal functionality of commonly used circuits or building blocks like buffer amplifiers and opamps. We were able to overcome these problems and developed a library of digital and analog building blocks based on the modeling of cryogenic behavior, and on adapted design and layout techniques. These techniques have been validated in an automated cryogenic test set-ups developed at IMEC. We will present here in detail the full design of the 18 channel CRE circuit, its interface with the Ge:Ga sensor, and its electrical performance and demonstrate that all major specifications at 4.2 K were met. Future designs and implementations will be equally presented.

A 4.2 K readout channel in a standard 0.7 /spl mu/m CMOS process for a photoconductor array camera

Abstrsct:The cryogenic design of a cold CMOS readout channel to be used in the Photoconductor Array Camera and Spectrometer (PACS) aboard the Herschel Space Observatory (HSO, formerly called FIRST) [I], is presented. Robust architectures and optimized sizing reduce the effect of cryogenic anomalities on the circuit. Simulation results and tests, both at room temperature and 4 K show a non-linearity < 2%, a hysteresis of <5mV and noise < 100nV/H~”~ @ 30Hz.

Flight Qualification and Circuit Development of Sensor Front-End Electronics for PACS/Hershel at Liquid Helium Temperature

In the framework of the development of the European Space Agencys Herschel Space Observatory (HSO), IMEC designed the cold-readout electronics (CRE) for the PACS instrument. Key specifications for this circuit were high linearity, low power consumption, high uniformity, and very low noise at an operating temperature of 4.2K (liquid helium temperature, LHT). To ensure high production yields and uniformity, relatively easy availability of the technology, and portability of the design, the circuit was implemented in a standard CMOS technology. The circuits are functional at room temperature, which allows screening prior to integration and qualification and has an important impact on the production yield and time. The circuit was mounted on an Al2O3 substrate for optimum electrical performance. On the same substrate, bias signal generation, short-circuit protection circuitry, and decoupling capacitors for the power lines were integrated. This led to a relatively complex substrate containing over 30 passives ...