We present a method to characterize the temperature dynamics of miniaturized thermal IR sources. The method circumvents the limitations of current IR photodetectors, by relying only on an electrical measurement rather than on optical detection. Thus, it enables the characterization of the light emission of IR sources over their full operation frequency range. Moreover, we develop a model of thermal IR sources allowing simulations of their thermal and electrical behavior. By combining measurements and modeling, we achieve a comprehensive characterization of a Pt nanowire IR source: the reference resistance R0 = 17.7Ω, the TCR α = 2.0 × 10-3 K-1, the thermal mass C = 2.7 × 10-14 J/K, and the thermal conductance G = 1.3 × 10-6 W/K. The thermal time constant could not be measured, because of the frequency limitation of our setup. However, the operation of the source has been tested and proved to function up to 1 MHz, indicating that the thermal time constant of the source is smaller than 1 μs.
Most of today's commercial solutions for un-cooled IR imaging sensors are based on resistive bolometers using either
Vanadium oxide (VOx) or amorphous Silicon (a-Si) as the thermistor material. Despite the long history for both
concepts, market penetration outside high-end applications is still limited. By allowing actors in adjacent fields, such as
those from the MEMS industry, to enter the market, this situation could change. This requires, however, that
technologies fitting their tools and processes are developed. Heterogeneous integration of Si/SiGe quantum well
bolometers on standard CMOS read out circuits is one approach that could easily be adopted by the MEMS industry.
Due to its mono crystalline nature, the Si/SiGe thermistor material has excellent noise properties that result in a state-ofthe-
art signal-to-noise ratio. The material is also stable at temperatures well above 450°C which offers great flexibility
for both sensor integration and novel vacuum packaging concepts. We have previously reported on heterogeneous
integration of Si/SiGe quantum well bolometers with pitches of 40μm x 40μm and 25μm x 25μm. The technology scales
well to smaller pixel pitches and in this paper, we will report on our work on developing heterogeneous integration for
Si/SiGe QW bolometers with a pixel pitch of 17μm x 17μm.
Cost efficient integration technologies and materials for manufacturing of uncooled infrared bolometer focal plane arrays
(FPA) are presented. The technology platform enables 320x240 pixel resolution with a pitch down to 20 μm and very
A heterogeneous 3D MEMS integration technology called SOIC (Silicon-On-Integrated-Circuit) is used to combine high
performance Si/SiGe bolometers with state-of-the-art electronic read-out-integrated-circuits.
The SOIC integration process consists of: (a) Separate fabrication of the CMOS wafer and the MEMS wafer. (b)
Adhesive wafer bonding. (c) Sacrificial removal of the MEMS handle wafer. (d) Via-hole etching. (e) Via formation and
MEMS device definition. (f) Sacrificial etching of the polymer adhesive. We will present an optimized process flow that
only contains dry etch processes for the critical process steps. Thus, extremely small, sub-micrometer feature sizes and
vias can be implemented for the infrared bolometer arrays.
The Si/SiGe thermistor is grown epitaxially, forming a mono-crystalline multi layer structure. The temperature
coefficient of resistance (TCR) is primarily controlled by the concentration of Ge present in the strained SiGe layers.
TCR values of more than 3%/K can be achieved with a low signal-to-noise ratio due to the mono-crystalline nature of the
material. In addition to its excellent electrical properties, the thermistor material is thermally stable up to temperatures
above 600 °C, thus enabling the novel integration and packaging techniques described in this paper.
Vacuum sealing at the wafer level reduces the overall costs compared to encapsulation after die singulation. Wafer
bonding is performed using a Cu-Sn based metallic bonding process followed by getter activation at ≥350 °C achieving a
pressure in the 0.001 mbar range. After assembling, the final metal phases are stable and fully compatible with hightemperature
processes. Hermeticity over the product lifetime is accomplished by well-controlled electro-deposition of
metal layers, optimized bonding parameters and a suitable bond frame design.
A technique for 3-D selective imaging of sound sources is described analytically and demonstrated experimentally. One-dimensional recordings of the acoustic field is measured using laser vibrometry. By applying digital holographic and tomographic algorithms to the acquired 1-D data, the full 3-D complex amplitude is reconstructed. The use of multiple frequencies in the spectral content of the acoustic field gives a number of advantages: higher spatial resolution, less noise in the reconstructed image, less sensitivity to noise in the measurements, and the possibility to perform selective imaging. Theory for all three steps—the measurement of sound using light, numerical propagation of waves, and finally the tomographic reconstruction in the process are given. In the experiment, the positions of three ultrasound sources are accurately determined and two different types of transducers are distinguished from each other. This multiwavelength technique could show to be a useful addition to optoacoustic imaging.
Using X-rays as information carriers it is possible to obtain data about motion inside an object that is opaque to visible light. An image correlation algorithm can be applied to a set of two X-ray images taken sequentially during a process, where the interior of the object is in motion. A displacement field describing the projected intermediate motion is thus obtained to sub-pixel accuracy. If this image set is expanded to contain several pictures separated in time, together describing the whole process, the images can be sequentially correlated to obtain a dynamic displacement field. In this paper, dynamical displacement field measurements have been carried out on two different objects, the first being a silo, where the motion of the flowing material in the center plane is investigated. In the second case, the motion in a layer of glue between two wooden plates is examined during a process where a shearing force acts on the system. The plane in which the measurements are carried out is defined by the use of a contrast agent, usually a tungsten powder seeding. The obtained displacement field, together with the known intermediate time interval between exposures, gives the velocity field in the seeded plane. The results show good agreement with the expected motion in the respective processes, but also provide evidence of behavior that would be undetectable using other existing techniques. A third experiment has also been carried out on a material requiring no contrast enhancing media. These measurements were performed on a chicken thigh being deformed by an external force. The results will be discussed in relation to their reliability and applicability. Further, the direction of future research will be indicated.