Ultrathin 2 nm gold as ideal impedance-matched absorber for infrared light

Thermal detectors are a cornerstone of infrared (IR) and terahertz (THz) technology due to their broad spectral range. These detectors call for suitable broad spectral absorbers with minimalthermal mass. Often this is realized by plasmonic absorbers, which ensure a high absorptivity butonly for a narrow spectral band. Alternativly, a common approach is based on impedance-matching the sheet resistance of a thin metallic film to half the free-space impedance. Thereby, it is possible to achieve a wavelength-independent absorptivity of up to 50 %, depending on the dielectric properties of the underlying substrate. However, existing absorber films typicallyrequire a thickness of the order of tens of nanometers, such as titanium nitride (14 nm), whichcan significantly deteriorate the response of a thermal transducers. Here, we present the application of ultrathin gold (2 nm) on top of a 1.2 nm copper oxide seed layer as an effective IR absorber. An almost wavelength-independent and long-time stable absorptivity of 47(3) %, ranging from 2 $\mu$m to 20 $\mu$m, could be obtained and is further discussed. The presented gold thin-film represents analmost ideal impedance-matched IR absorber that allows a significant improvement of state-of-the-art thermal detector technology

Input and intrinsic device modeling of VCSELs

An efficient model scheme that combines the non-linear behavior of the input parasitics with the intrinsic fundamental device rate equations of the Vertical Cavity Surface Emitting Lasers (VCSELs) is proposed. A systematic methodology for the model parameter extraction from dc and ac, electrical and optical measurements, is also presented and simulation results are compared with the experimental measurements. Extraction and simulation procedures are implemented in commercial integrated circuit design tools and they are proved to be very fast while they preserve adequate accuracy. © Springer Science+Business Media LLC 2007

A compact nonlinear equivalent circuit model and parameter extraction method for packaged high-speed VCSELs

A compact nonlinear circuit model for the input of packaged high-speed vertical-cavity surface-emitting lasers (VCSELs) is presented in this paper. The model includes the thermal effects as well as the parasitics, due to the various levels of the packaging hierarchy, to ensure a realistic representation of the input of the VCSELs. The values of the model parameters are extracted from dc current-light-voltage characteristics and S11 vector measurements using a two-step parameter extraction procedure. Extraction of the model parameters and comparison between measured and simulated results have been performed for two different commercially available VCSELs operating at 2.5 Gb/s. The achieved agreement between the measured and simulated results is very satisfactory for the dc as well for the S11 curves in the frequency range from 3 MHz to 3 GHz. © 2004 IEEE

Driving high-speed VCSELs

A comparison of the small-signal and transient responses of high-speed VCSELs using ideal as well as realistic current and voltage drivers is performed. A nonlinear VCSEL equivalent model is implemented and the associated parameters are extracted from the dc and ac measurements of a commercially available packaged device. The simulations, using the extracted realistic VCSEL models, show that the employment of voltage drivers results in an improvement of 74% of the 3-dB cutoff frequency of the optical-current signal. Moreover, an 80% reduction of the rise and fall time and a 66% reduction of the signal delay are observed. © 2004 Wiley Periodicals, Inc

Flexible monolithic active pixel sensors embedded in ultra thin polymer film

A CMOS Monolithic Active Pixel Sensor (MAPS) integrates on the same silicon substrate the radiation sensor element (thin epitaxial layer) with processing electronics (based on CMOS transistors) on top. Total thickness of active volume of this stack is usually very small: typically 15 m for silicon and 5 m for interconnections (several metal-insulator layers). Excellent minimum ionizing particle tracking performance has been demonstrated with these devices and recent availability of high-resistivity epitaxy allows them to reach radiation hardness comparable to standard, fully depleted silicon sensors. MAPS can be thinned down to less than 30 m, without loosing their tracking performance. This allows not only very small material budget but also construction of non-planar detector layer: such thin silicon is flexible enough and can be bended to form a cylinder with a radius of the order of centimeter. However the structure is fragile, difficult to handle and to connect using standard methods (wire bonding). We propose a new method of packaging of such thin devices based on embedding in thin polymer film, with an application of modern silicon wafer processing technologies. In this solution, the sensor is protected from both sides by plastic material (10-20 m thick, insulator); metal paths deposited on top and directly connected to bonding pads through integrated vias in the polymer provide electrical connection. High-precision sensor Mimosa-18 (10 m pitch, 512x512 pixel array) has been chosen for the embedding process demonstrator. In this work, we present details of embedding process together with study of tracking performance of the sensor (charge collection properties, ENC, S/N ratio for MIPs) as a function of mechanical stress (bending). Possible extension of embedding process to larger area (tens of cm), multi-sensor structures and more than one metal layer interconnections will be also proposed and discussed

Recent ROB developments on wide bandgap based UV sensors

The next ESA spatial mission planned to study the Sun, Solar Orbiter (SO), necessitates very innovative EUV detectors. The commonly used silicon detectors suffer important limitations mainly in terms of UV robustness and dark current level. An alternative comes from diamond or III-nitride materials. In these materials, the radiation hardness, solar blindness and dark current are improved due to their wide bandgap. This paper presents the new developments on wide bandgap materials at the Royal Observatory of Belgium (ROB). We present also the LYRA instrument, the BOLD project, and the EUI instrument suite