The proper usage of a bandwidth-limited imaging bolometer for the measurement of the lateral temperature profile of microstructures in Silicon-Carbide (SiC) is analyzed. The SiC spectral emissivity, (Formula presented.), has a dip at (Formula presented.) (Formula presented.) m, which is in the band of a typical commercially available instrument and complicates the selection of the value of the equivalent emissivity, (Formula presented.), in the instrument settings. The impact is analyzed by deduction using simulation, and by experimental validation. Membranes of 3C-SiC of 1000 (Formula presented.) m diameter and 3 (Formula presented.) m thickness have been fabricated on Si wafers, with integrated poly-SiC resistors for both membrane heating and on-membrane temperature measurement for calibration purposes. The optimum setting was found as (Formula presented.) = 0.705 ± 0.025 by deduction and as (Formula presented.) = 0.66 ± 0.06 by experimental validation in the temperature range 120 °C to 400 °C. The apparent temperature coefficient of emissivity, (Formula presented.) 2 × 10 ⁻⁴ °C ⁻¹ is due to the shift of the Wien peak wavelength relative to the instrument’s sensitivity band.

The use of masked UV (i-line) lithography in a MEMS foundry for CMOS-compatible fabrication of large-area metasurface-based absorbers for the mid-infrared is demonstrated. The challenges are in: (a) the limited number of acceptable metals, (b) the thickness tolerance of the layers used in the CMOS process, and (c) the imaging capabilities of i-line lithography as compared to e-beam. The claimed throughput advantage with manageable distortion of masked lithography and the suitability of the layers used in a CMOS-compatible process in the fabrication of mid-IR absorbers was tested. Issues investigated are: (a) the impact of aluminium as the preferred metal in the MIM patch on the plasmonic response, (b) the influence of SiO₂ as preferred dielectric material, (c) the effect of corner rounding and horizontal-vertical bias of the masked lithography and (d) measures that can be taken during the design phase to mitigate any such detrimental effect. Based on the findings, disk-shaped patches are identified as the most suitable for shape-tolerant design. Metasurfaces with a unit-cell side-length of 3μm were fabricated over a chip area larger than 10⁵μm². Measurements do confirm that (a) aluminium is a suitable CMOS-compatible material for mid-IR metamaterial absorber fabrication, (b) a large surface roughness results in widening of the absorption peaks and (c) the typical layer thickness tolerance used in a MEMS foundry is also acceptable for mid-IR metasurface fabrication. Masked lithography limits the minimum design wavelength to about 3.5μm, while the surface roughness Rq ~ 5nm results in a bandwidth up to FWHM = 400nm.

In this paper, the growth of optimized vertically aligned multi-walled carbon nanotube (VA-MWCNT) forests by LPCVD method for use in a large-area absorber in infrared detectors is presented. The effect of synthesis temperature (500−700 °C) and time (1−10 min) on the optical absorption coefficient in the infrared (2−20 μm) is investigated by FT-IR measurement at various incident angles (15-80°). The structural properties of VA-MWCNT are characterized by SEM, TEM and Raman spectroscopy. Spectral measurements show an increasing absorption with the height of the forest that results at increased synthesis time and temperature. However, the absorption coefficient decreases with increasing synthesize time and temperature, while it is also affected by other properties, such as diameter, density, alignment, and uniformity. Moreover, the reduction in absorption at oblique incident angles demonstrates the relevance of surface properties. Finally, a circular graphite waveguide system is used to model the absorption characteristics of an MWCNT forest.

Ensuring optical transparency over a wide spectral range of a window with a view into the tailpipe of the combustion engine, while it is exposed to the harsh environment of sootcontaining exhaust gas, is an essential pre-requisite for introducing optical techniques for long-term monitoring of automotive emissions. Therefore, a regenerable window composed of an optically transparent polysilicon-carbide membrane with a diameter ranging from 100 µm up to 2000 µm has been fabricated in microelectromechanical systems (MEMS) technology. In the first operating mode, window transparency is periodically restored by pulsed heating of the membrane using an integrated resistor for heating to temperatures that result in oxidation of deposited soot (600–700 °C). In the second mode, the membrane is kept transparent by repelling soot particles using thermophoresis. The same integrated resistor is used to yield a temperature gradient by continuous moderate-temperature heating. Realized devices have been subjected to laboratory soot exposure experiments. Membrane temperatures exceeding 500 °C have been achieved without damage to the membrane. Moreover, heating of membranes to ΔT = 40 °C above gas temperature provides sufficient thermophoretic repulsion to prevent particle deposition and maintain transparency at high soot exposure, while non-heated identical membranes on the same die and at the same exposure are heavily contaminated.

This article describes the fabrication of MgF₂ and MgO thin-film-based optical filters and compares the optical transmission of the filters over UV. The MgF₂ thin-films were deposited by use of an e-beam technique and their optical properties were characterised by ellipsometry. The effect of substrate temperature on the optical properties was studied. The MgF₂ optimum refractive indices were obtained with a substrate temperature between 200 °C and 300 °C. Optical simulations were performed to compare the performance of MgF₂ and MgO in the fabrication of near-UV narrow bandpass optical filters. While MgO-based optical filters result in a higher transmittance peak intensity, especially at 350 nm, the MgF₂ optical filters are narrower, present lower values of FWHM, a mean value of 20 nm. This feature could be especially relevant for specific applications on fluorescent optical sensors. Finally, a Fabry-Perot based on a MgF₂/TiO₂ optical filter was deposited, using an e-beam technique for the MgF₂ thin-films and RF-sputtering technique for the TiO₂ thin-films. The MgF₂/TiO₂ optical filter peak transmittance is approximately 70% close to 400 nm, as expected. The results are discussed with focus on applications in fluorescent optical sensors for peaks at 350, 370, 380 and 400 nm, respectively.

Decision-making on the optimum transition pathway to an energy economy that meets agreed carbon reduction goals in the European Union (EU) by 2050 is challenging, because of the size of the infrastructural legacy, technological uncertainties, affordability and assumptions on future energy demand. This task is even more complicated in transportation because of additional issues, such as minimum travel range at acceptable impact on payload and ensuring hazzle-free long-distance driving in case of regionally varying fuel economies. Biofuels were the first viable option for a large-scale partly renewable fuel economy. E10 and B7 fuels have been successfully and remarkably smoothly introduced, owing to the fact that these are liquid and can be used in conventional combustion engines with little impact on full-tank travel range. In contrast, the decision-making process on biofuels in the EU has been particularly turbulent, with an initially favourable assessment changing into controversial. Here the compatibility between the fuel economies of member states and avoidance of disruptive social effects are considered as essential pre-requisite of a viable transition pathway. Rebalancing three different aspects of the social dimension of sustainability is used to demonstrate that a succession of infrastructures based on liquid fuels, with biofuels as an interlock towards an economy that includes methanol-based eFuel, has the potential to bring continuity, reduce dependence on anticipated technological advances and improve cost management. Awareness of this underexposed prospect of biofuel may positively affect the assessment on its role in a low-carbon fuel economy, potentially influencing the current decision-making process on biofuels.

Exhaust gas measurement in the harsh environment of the tailpipe by optical techniques is a highly robust technique, provided that optical access is maintained in the presence of soot. The design, fabrication, and testing of membranes in SiC-on-Si with integrated heaters to serve as a regenerable MEMS optical window into the tailpipe are presented. Membranes at slightly elevated temperatures are demonstrated to keep the surface transparent by thermophoresis, while surface regeneration is achieved at pulsed high temperatures, which allows long-term optical measurement in the exhaust.

The resistive particulate matter sensor is a simple device that transduces the presence of soot through impedance change across inter-digital electrodes (IDEs). We investigate the information provided by impedance spectroscopy over the frequency range from 100 Hz to 10 kHz for two purposes. The first is to investigate the opportunities for an improved sensor response to particulate matter (PM), based on the additional information provided by the measurement of both the in-phase (resistive) and out-of-phase (capacitive) components of the change in impedance over this frequency range as compared to DC resistance measurement only. Secondly, the origin of the capacitive response of the device is investigated from the perspective that soot on the device is in the form of bendable dendrites that grow in three dimensions. An IDE structure with the housing acting as an additional suspended electrode for introducing a controllable vertical electric field component has been used for this purpose. The formation of dipoles, due to bending of the charged dendrites, is found to be the source of the capacitive response. Simulation of electrostatic soot deposition reinforces dendritic self-assembly mechanisms, driven by charged particle trajectories along electric field lines. Optical microscopy confirms that dendrites growing out of the substrate plane are sensitive to electric and flow forces, bending when force balances are appropriate. We also apply impedance spectroscopy under varying electric field strengths, showing that capacitive response is only observed when conditions are conducive to dendrite bending in response to the applied AC electric fields.

A suspended polySi heater is presented for use as a mid-IR light source in a microspectrometer based on a linearly variable optical filter (LVOF). Distributed electrical powering of a segmented structure with a specially designed suspension system is used for obtaining a temperature profile that is constant over the length of the element with a peak temperature significantly higher as compared to the conventional on-chip hot-wires. The integrated LVOF design results in an enhanced spectral emission and facilitates the use in the composition measurement of liquids and gases by absorption spectroscopy.

Minimally invasive medical devices can greatly benefit from Narrow Band Imaging (NBI) diagnostic capabilities, as different wavelengths allow penetration of distinct layers of the gastrointestinal tract mucosa, improving diagnostic accuracy and targeting different pathologies. An important performance parameter is the light intensity at a given power consumption of the medical device. A method to increase the illumination intensity in the NBI diagnostic technique was developed and applied to minimally invasive medical devices (e.g., endoscopic capsules), without increasing the size and power consumption of such instruments. Endoscopic capsules are generally equipped with light-emitting diodes (LEDs) operating in the RGB (red, green, and blue) visible light spectrum. A polydimethylsiloxane (PDMS) µ-lens was designed for a maximum light intensity at the target area of interest when placed on top of the LEDs. The PDMS µ-lens was fabricated using a low-cost hanging droplet method. Experiments reveal an increased illumination intensity by a factor of 1.21 for both the blue and green LEDs and 1.18 for the red LED. These promising results can increase the resolution of NBI in endoscopic capsules, which can contribute to early gastric lesions diagnosis.

This paper presents the results of in vitro photodynamic therapy assays on RKO and HCT-15 cell lines. The envisaged implementation is in autonomous medical microdevices, such as endoscopic capsules for clinical treatment of several types of gastrointestinal tract tumors. Because of their very limited device volume, light fluence and fluence rate needed to destroy tumor cells should be minimized. Foscan or meta-tetra(hydroxyphenyl)chlorin (mTHPC) is used as a photosensitizer. The experimental results show that a small amount of mTHPC (0.15 mg/kg) and light fluence (5-20 J/cm²) is sufficient to obtain significant photodynamic activity. An array of LEDs with peak transmittance at 652 nm is used as a portable light source for the maximum quantum efficiency in producing singlet oxygen. Irradiation to a light fluence between 2.5 and 10 J/cm² is achieved by an increased exposure time at an 11 mW/cm² light fluence rate, while mTHPC concentrations of 0.5, 1, 5, and 10 μg/mL are used. The experimental results show that decreased cell viability (down to 30%) can be obtained for 1-5 μg/mL of mTHPC concentrations and 2.5 J/cm² of light fluence. Such light fluence and light fluence rate are compatible with the endoscopic capsules batteries.

The design of a mid-infrared micro-spectrometer based on an array of differently tuned narrow-band metamaterial absorbers is presented. The spectral response is tailored by the design of the unit cell. Each spectral band is composed of a thermopile detector with a 300 ×180 μm² Al-based metamaterial absorber fabricated in a CMOS compatible post-process. The challenges in the fabrication of the sub-μm features within the unit cell over a several mm² absorber area by equipment that is part of the standard infrastructure of a MEMS facility is addressed. The design and fabrication method utilized here for the first time enables the CMOS fabrication of integrated large-area plasmonic components on thermal detectors.

Optical coherence tomography (OCT) systems have huge potential for applications beyond the traditional ophthalmology as a general-purpose medical instrument for optical biopsy. The widening of the range of applications is expected to significantly increase production volume and, consequently, puts pressure on unit cost. This trend calls for a flexible and miniaturized system fabricated in a batch process. In this paper, the different OCT configurations are compared for suitability in such an implementation. The required flexibility favors operation in the spectral domain, using a broadband light source in combination with a spectrometer, while the miniaturization and low unit-cost in batch fabrication can be achieved using silicon micro-system technologies. The feasibility of miniaturizing OCT components has already been demonstrated, amongst others a beam splitter using 45° saw dicing of a glass substrate and appropriate thin-film coating the integration of the essential components into a single OCT microsystem remains a challenge. In this paper, the wafer-level fabrication of a Michelson interferometer for a miniaturized OCT system is presented, using an improved 45° saw dicing process, which is suitable for wafer-level co-integration of also the other components of the OCT microsystem.

The design and fabrication of wideband mid-infrared metamaterial absorbers are presented. The emphasis is put on the shape-tolerant design for using masked UV (i-line) lithography and CMOS-compatible fabrication to enable on-chip co-integration with detector and readout circuits in a MEMS foundry while maintaining wafer throughput. The CMOScompatibility implies the use of aluminum rather than the commonly used high conductivity metals. The use of masked lithography rather than e-beam lithography in the fabrication of metamaterial absorbers for the mid-infrared range between 3 and 4 μm introduces the challenge of the shape-tolerant design of the unit cell. Moreover, the sensitivity of the fabricated metamaterials to the surface roughness and exposure dose were investigated in this paper. The throughput advantage of masked lithography has been exploited in the fabrication of mid-infrared absorbers over an area of several mm². The measurements confirm the theoretical spectral response and a 98% peak absorption at an angle close to perpendicular incidence. Measurements at different angles show that the absorption spectrum only deviates marginally from normal incidence for angles up to 30°. The combined CMOS-compatibility and masked lithography enable batch fabrication and the on-chip integration of the metamaterial absorbers with MEMS devices and sensors.