In this paper, we demonstrate a novel, cost-effective sensing system utilizing a molecularly imprinted polymer (MIP) for the indirect colorimetric detection of 2-methoxphenidine (2-MXP). Unlike other colorimetric methods that often require expensive spectrometers and bulky read-out equipment, our system is streamlined, employing basic components such as a digital RGB colour sensor, a white LED, and a 3D-printed opaque enclosure compatible with standard spectrometer cuvettes. The sensor is constructed from readily available commercial components using conventional manufacturing processes. Our approach is versatile, accommodating various liquid analytes, making it suitable for diverse applications, including rapid toxicological screening. To this end, optimization towards the dwell time, number of assays needed, and a dose response for the methodology are explored. Specifically, we focus on the detection of 2-MXP in an aqueous solution within a concentration range of 0.05 to 1 mM. Within range, our system effectively identifies the presence of the analyte and quantifies its concentration. Notably, we achieved a detection limit as low as 0.026 mM, which corresponds to a typical metabolite concentration observed in humans. These results underscore the potential of our prototype sensor for practical applications in the rapid and economical field of diagnosis of MXP intoxication.

This work presents the results of the development of a 355 nm nano-second UV laser ablation process for silicon wafer singulation. The study focuses on the two most prevalent crystal orientations in semiconductor manufacturing: Si (100) and Si (111). The developed laser ablation process is purely dry, doesn't require any liquid, vapor phase or plasma and minimizes particles generation in the close vicinity of the dicing street. This process is specifically suitable for applications involving wafers sensitive to liquid exposure and particles contamination. Notable examples include MEMS devices and metal-oxide (MOX) micro-hotplate gas analyzers, where conventional blade dicing with constant water flow may cause irreversible damage to delicate structures and functionalized layers, as well as introduce contamination. The proposed alternative - UV laser ablation singulation technique achieved a narrow $36 \mu \mathrm{m}$ kerf width on $525 \pm 25 \mu \mathrm{m}$ thick Si (100) and Si (111) wafers. The process achieved an aspect ratio (cutting depth to kerf width) of approximately $15: 1$. Notably, no chipping on the face and backside of the wafer were observed. Furthermore, despite inherent variations in laser-ablated groove depth, cutting performance showed no statistically significant difference between $\text{Si}(100)$ and $\text{Si}(111)$ wafers.

A typical process flow for micro-hotplate sensors includes the fabrication of the sensor wafer followed by functionalization. Functionalization involves the local deposition of a sensing material, or several materials in the case of a multi-gas analyzer. Functionalization makes the analyzer sensitive to specific gases. Typically, functionalization is a wafer-level process, of which screen and inkjet printing, dispensing and direct atomic layer processing are good examples. Once the sensor wafer is fully processed and functionalized, it must be singulated onto individual sensor dies. After that the individual sensor die will be assembled. Various die singulation methods have been reported, but they can pose serious problems for the functionalized sensor wafer. The sensing materials used for functionalization are dominated by metal-oxides, which are sensitive to environmental factors, including thermal exposure, humidity uptake, etc. In this paper, we reviewed various die singulation techniques and methods, in function of their suitability for singulating fully functionalized metal-oxide (MOX) micro-hotplates sensor silicon wafers, including wafer sawing, laser ablation and dicing, scribe-and-break, stealth dicing, plasma dicing, dicing before grinding and others. Finally, we identified the most suitable wafer singulation method for the selected application and presented an outlook.

Colorimetric characterisation systems based on LEDs and RBG sensors are straightforward to implement, are highly integrable allowing for portable measurement systems and can be constructed using widespread and affordable components. They have already proved to be a satisfactory solution in several applications related to chemical analysis. In this paper, we present an RGB sensor-based prototype for colorimetric characterisation, which can accommodate cuvettes with optical paths of 10 mm and 40 mm. We assessed the impact of experimental condition parameters such as the variability of the analyte volume in the cuvette, as well as the presence of floating particles or deposits at the bottom of the cuvette. While these would not impact the result given by a spectrophotometer that generally has a directional light source, they must be considered in LED/RGB sensor analysers in which the light path is not tightly controlled. We demonstrated that there is a minimal sensor height above the bottom of the cuvette and a minimal analyte level (both depending on the prototype optical path length) above which the analyte volume and the presence of floating particles and deposits have no impact on the prototype output signal. Finally, based on these results, we proposed a test method for a quick dye-displacement assay, in which the reagent is a dye-loaded molecularly imprinted polymer that is poured directly into a cuvette.

We designed a 3D geometrical model of a metal-oxide gas sensor and its custom packaging and used it in finite element modeling (FEM) analysis for obtaining temperature and heat flux distribution. The 3D computer simulation, performed with GetDP software (version 3.5.0, 13 May 2022), accurately predicted the temperature distribution variation across the entire assembly. Knowing the temperature variation and the location of the hot spots allowed us to select the best electrical interconnect method and to choose the optimal materials combination and optimal geometry. The thermal modeling also confirmed the need to use a low thermal conductivity material to insulate the MOX sensor since the latter is heated to its operational temperature of 250 °C. For that purpose, we used the in-house formulated xerogel–epoxy composite of thermal conductivity of 0.108 W m−1 K−1, which is at least 30% less compared to the best-in-class among commercially available materials. Based on the 3D FEM outputs, we designed, assembled, and characterized a fully functional packaged MOX gas sensor in several configurations. We measured the temperature distribution on all parts of the MOX gas sensor assembly using a thermal imaging infrared (IR) microscope. The results of 3D FEM are in good agreement with the temperature distribution obtained by the non-contact IR thermal characterization.

In this paper, we presented a novel, compact, conceptually simple, and fully functional low-cost prototype of a pH sensor with a PANI thin film as a sensing layer. The PANI deposition process is truly low-cost; it performs from the liquid phase, does not required any specialized equipment, and comprises few processing steps. The resulting PANI layer has excellent stability, resistance to solvents, and bio- and chemical compatibility. The pH sensor’s sensing part includes only a few components such as a red-light-emitting diode (LED) as a light source, and a corresponding photodiode (PD) as a detector. Unlike other PANI-based sensors, it requires no sophisticated and expensive techniques and components such lasers to excite the PANI or spectrometry to identify the PANI color change induced by pH variation. The pH sensor is sensitive in the broad pH range of 3 to 9, which is useful for numerous practical applications. The sensor requires a tiny volume of the test specimen, as little as 55 µL. We developed a fully integrated packaging solution for the pH sensor that comprises a limited number of components. The pH sensor comprises exclusively commercial off-the-shelf (COTS) components and standard printed circuit boards. The pH sensor is assembled using standard surface mounting technology (SMT).

This article presents a review of device processing technologies used in the fabrication of biomedical systems, and highlights the requirements of advanced manufacturing technology. We focus on biomedical systems that perform diagnostics of fluidic specimens, with analytes that are in the liquid phase. In the introduction, we define biomedical systems as well as their versatile applications and the essential current trends. The paper gives an overview of the most important biomolecules that typically must be detected or analyzed in several applications. The paper is structured as follows. First, the conventional architecture and construction of a biosensing system is introduced. We provide an overview of the most common biosensing methods that are currently used for the detection of biomolecules and its analysis. We present an overview of reported biochips, and explain the technology of biofunctionalization and detection principles, including their corresponding advantages and disadvantages. Next, we introduce microfluidics as a method for delivery of the specimen to the biochip sensing area. A special focus lies on material requirements and on manufacturing technology for fabricating microfluidic systems, both for niche and mass-scale production segments. We formulate requirements and constraints for integrating the biochips and microfluidic systems. The possible impacts of the conventional microassembly techniques and processing methods on the entire biomedical system and its specific parts are also described. On that basis, we explain the need for alternative microassembly technologies to enable the integration of biochips and microfluidic systems into fully functional systems.

In some specific microelectronic applications, there is a demand for adhesive materials (glues/encapsulants) having very good thermal insulation properties. We have studied the properties obtained on epoxy-based samples loaded by several levels of xerogel filling. The thermal conductivity of these materials depends on the exact chemical composition and their manufacturing process. As a result, the thermal conductivity given in the manufacturer's specifications or in the literature generally exhibits some dispersion. Therefore, we have developed a straightforward experimental rig, based on a vacuum chamber and miniature Pt100 sensors measurements, to precisely know the thermal conductivity of the various insulating materials used in the development and the assembly of select microsensors and microsystems. The results showed a decrease in the thermal conductivity of our xerogel-epoxy composites up to 35.8% compared with the value of the unfilled epoxy, corresponding to a thermal conductivity value of 107.9 mW m(-1) K-1. In addition, cross-sectional images were observed by optical microscopy to characterize the specific microstructure of each sample to relate these observations to improvements in thermal conductivity.

Metal-oxide (MOX) gas sensors commonly rely on custom packaging solution. With an ever-increasing demand for MOX gas sensors, there is a clear need for a low cost, compact and high-performance package. During normal operation, MOX sensors are heated up to a temperature in the typical range of 200-300°C. However, the generated heat must not damage or degrade any other part of the assembly. Using 3D finite elements modelling, we developed an optimal package configuration. To thermally insulate the assembly from the heated MOX sensor we have developed in-house a low thermal conductivity xerogel-epoxy composite with 22.7% by weight xerogel and a thermal conductivity of 107.9 mW m−1 K−1 which is a reduction exceeding 30% compared to commercially available epoxy. Based on the low thermal conductivity xerogel-epoxy composite, we have developed a novel packaging approach that can suit the large family of MOX sensors. The developed alternative packaging solution includes a small number of assembly steps and uses standard processes and techniques. The assembled MOX sensor is low cost and has a low power consumption, while all thermally sensitive assembly parts remain at low temperature during the system’s lifetime.

This article presents a tamper detection sensor complementing cryptographic techniques in order to protect data from unauthorized access and/or from data falsification. Both the mechanical and electronic parts of the systems are described. The proposed architecture targets portable devices and can be realized using commercially available components, widely available materials and known manufacturing and assembly techniques. The tamper detection circuit is based on a capacitive sensing principle and uses ultra-low-power electronic components, leading to an overall consumed current below $10~\mu \text{A}$ . Autonomy is a crucial reported drawback of miniaturized battery backed-up anti-tampering hardware systems: the presented architecture and implementation ensures a lifetime of at least 3 years when powered by one CR2032 coin cell battery. The paper also assesses the sensitivity of the tamper detection: measurements show that the system is able to detect a variation of at least one percent of the capacitance of the tamper layer, resulting from an attempt to breach the outer shell surrounding the circuit for accessing the sensitive data.

The paper reports on fabrication processes related to low-cost manufacturing and integration of microfluidic biomedical detection systems fabricated without a cleanroom. First, we developed and demonstrated a process for manufacturing a microfluidic device. Second, we demonstrated a low temperature assembly technique for the packaging of the surface acoustic wave (SAW) sensor die. Sequentially, we demonstrated a low temperature process for the integration of the microfluidic device with a SAW sensor to form a fully functional biomedical detection system. The microfluidic device was manufactured by mechanical micromilling technology that is rapid, conceptually simple and a low-cost process. It is suitable for both prototyping and for a low and a medium scale production to address a niche market that is typical for the intended application. That technology has no specific requirement for a certified clean room environment. Unlikely other technology, such as molding and photolithography, for example, it has a shorter lead-time from design to manufacturing. The assembly technique for a SAW sensor is a carefully selected combination of known and matured processing steps causing no damage to a sensitive biofunctionalization on the sensor. The developed and demonstrated integration process for the in-house manufactured microfluidic device and the SAW sensor is a purely low temperature process that prevents a biological material deposited on the SAW sensor from degradation. Biocompatibility issues were also addressed during the study reported. Finally, we performed an ultrasonic (US) impedance characterization of the fully assembled system and demonstrated that neither the microfluidic system integrated on the sensor nor the integration process itself have an impact on the US impedance of the SAW sensor. That means that it does not affect the sensor performance. (c) 2021 Elsevier B.V. All rights reserved.

We have developed a straightforward die-level thinning process suitable for Silicon-On-Insulator (SOI) dies. The process has been demonstrated on SOI CMOS die assembled on rigid and flexible PCBs using previously-developed anisotropic conductive adhesive flip-chip method. Unlike standard wafer-level thinning processes, in the demonstrated process the full thickness SOI die is directly mounted on PCB and after that thinned. The demonstrated process is simple and robust; it comprises fewer process steps compared to conventional die thinning process. The ultra-thinning process has no effects on the assembly integrity and device performance.

Following a demand for thermal management there is need to measure precisely a temperature on the most critical part of microassembly. The widely-used contact type of measurements is often not suitable for micro parts of assembly as small as 0.5 mm and smaller. The non-contact measurements currently available are not always directly applicable on complex heterogeneous microassemblies structures such as miniaturized metal-oxide (MOX) gas sensor. In response to this, we have developed a simple technique using IR thermography for accurate and non-contact temperature measurements of electronic microassemblies, and validate this approach with MOX sensors heated to operating temperature of 250-300°C.

This paper describes a hybrid mass sensing system comprising a QCM (quartz crystal microbalance) mass sensor operating under atmospheric pressure and a 3-DOF mode localized coupled resonator operating in vacuum. Nanoparticles as consecutive mass perturbations are added onto the QCM, the output signals with respect to the amount of mass change are then being manipulated to generate electrostatic forces. Subsequently, the electrostatic forces act on the 3-DOF mode localized coupled resonator as external stiffness perturbations. The output metrics of the hybrid system were defined as: the resonant frequency shifts, vibration amplitude changes, and the changes in resonance amplitude ratio. Measured data was analyzed for these metrics and compared. This work demonstrated that the proposed hybrid mass sensing system attained a 2.5×10 6 N(m · kg)-1 mass to stiffness transduction factor, and has the potential to be employed as a direct liquid contact biochemical transducer.

Laser direct copper patterning of fine pitch features on polyimide flexible substrate was investigated. On such thin substrates (generally below 0.1 mm), laser parameters should be optimized in order to minimize the damage beneath the conductive layer, as it might lead to severe robustness issues. We selected several parameter sets and compared them in terms of damage depth, feature sizes and edge straightness. On bare copper PCBs (Printed Circuit Boards), we managed to limit the average damage to a depth of 8 mu m, while getting features' characteristics significantly better than what would be obtained with standard chemical etching. We also demonstrated alternative parameter sets that allow to obtain ultra-thin features or very straight edges at the cost of deeper damage in the substrate. Two application cases were studied. Firstly, we realized 2D planar coils. Due to a higher number of turns at equivalent surface areas, laser patterning of a spiral coil results in inductance value one order of magnitude larger when compared with standard chemical etching (39 mu H vs. 4 mu H for a 113 mm(2) coil). Such coils can advantageously be used in sensing or inductive charging applications, when flexibility and/or ultra-thin profile is required. Secondly, we demonstrated the feasibility of fine-pitch bond pads for COF (Chip-On-Flex) applications. We achieved a bond pad pitch of 80 mu m (60 mu m pad dimension / 20 mu m pad clearance). Laser direct pattering is presented as a single step and purely dry alternative to high-end PCB manufacturing processes.

We developed a low-cost process for assembling versatile sensors without expensive, thick metal finish on rigid and flexible PCB using anisotropic conductive films (ACF) flip-chip (FC) process. This allows a lower temperature budget than conventional FC assembly. The ACF FC process requires no expensive set up, is quick to implement and suits perfectly for sensor prototyping and low-scale manufacturing. The process was directly applied to assemble the bare die of a CMOS strain gauge sensor on flexible PCB without compromising its integrity.

This article reports on laser technology based fabrication approach to develop a micro-size capacitive gap based transducer useful for a variety of applications. A low-cost prototype has been fabricated via a rapid and advanced laser micro-milling technique to achieve a parallel kerf-width (capacitive gaps) of about 60 µm into a piece of aluminum and a stainless steel each of 1 and 2 mm thickness, respectively, thus leading to a high-aspect ratio (> 33) structure. A device is demonstrated to facilitate actuation via electrostatic means and sense a capacitive change across its electrode. Experiments have been performed with a structure made of aluminum. Results comprising analytical modeling, fabrication, and electrical characterization are presented. An applicability of a device as a two degree-of-freedom resonating mode-localization sensor that employs a weak electrostatic coupling is demonstrated to offer vibration amplitude based sensitivity to a relative change in the stiffness. This sensor is able to resolve a minimum stiffness perturbation (normalized), $$\delta_{{k_{\rm{min} } }} = \frac{\Delta k}{{K_{eff} }}$$ of the order of 7.98 × 10−4.

Low-power wide-area network protocols, such as LoRa, Sigfox, and NB Internet of Things, have become a popular technology for long range and limited data communication. Those protocols have been optimized for low power consumption and offer competitive subscription prices. This article presents the development of an autonomous Sigfox sensor node capable of transmitting data collected by a range of sensors directly to the cloud. The device is powered by a solar cell and can transmit data every 5 min under cloudy conditions (<;5000 lx). Such a high transmission rate has not yet been reported in the literature for a fully autonomous system. Field trials have been realized by placing two sensor nodes at a vineyard in order to collect meteorological parameters.

This paper reports on a QCM (quartz crystal microbalance) mass sensor under atmospheric pressure that is combined with a 3-DOF micromachined coupled resonator operating in vacuum. With nanoparticles consecutively added on the QCM. the output signals from the QCM is then modified to produce electrostatic forces which are fed to a 3-DOF mode localized weakly coupled resonator. The 3-DOF coupled resonator hence utilizes the input electrostatic force as stiffness perturbations to perform the sensing operation. A comparison of three sensitivity characterization methods was carried out: resonance frequency shift, amplitude change and resonance vibration amplitude ratio. The results demonstrate that a 3-DOF mode localized coupled resonator incorporated with a QCM mass sensor has potential to be employed as a direct liquid contact biochemical transducer.

In this work, we developed and characterised an autonomous micro-platform including several types of sensors, an advanced power management unit (PMU) and radio frequency (RF) transmission capabilities. Autonomy requires integration of an energy harvester, an energy storage device, a PMU, ultra-low-power components (including sensors) and optimized software. Our choice was to use commercial off-the-shelf components with low-power consumption, low cost and compactness as selection criteria. For the multi-purpose micro-platform, we choose to include the most common sensors (such as temperature, humidity, luminosity, acceleration, etc.) and to integrate them in one miniaturised autonomous device.A processing unit is embedded in the system. It allows for data acquisition from each sensor individually, simple data processing, and storing and/or wireless data transmission. Such a system can be used as stand-alone, with an internal storage in a non-volatile memory, or as a node in a wireless network, with bi-directional communication with a hub device where data can be analysed further. According to specific application requirements, system settings can be adjusted, such as the sampling rate, the resolution and the processing of the sensor data.Parallel to full autonomous functionality, the low-power design enables us to power the system by a small battery leading to a high degree of autonomy at a high sampling rate. Therefore, we also developed an alternative battery-powered version of the micro-platform that increases the range of applications. As such, the system is highly versatile and due to its reduced dimensions, it can be used nearly everywhere. Typical applications include the Internet of Things, Industry 4.0, home automation and building structural health monitoring.