Heavy-metal-free III-V semiconductor-based colloidal quantum dots (CQDs), such as InAs, are promising candidates for near- and short-wave infrared detection. However, up-to-date research efforts remain mainly limited to wavelengths below 1100 nm due to challenges in synthesis, junction formation, and passivation for large diameter InAs quantum dots. Systematic investigations into device design, reverse dark current mechanisms, and trap distributions in larger InAs quantum dots remain limited. Here, we report a thin-film PIN heterojunction colloidal InAs (1200 nm) photodiode stack with amorphous indium gallium zinc oxide and copper(I) iodide transport layers. To the best of our knowledge, the device exhibits one of the lowest reported dark current densities of 4.7 μA/cm2 at -1 V and 298 K, which decreases to 3.6 nA/cm2 at 220 K. Temperature-dependent current-voltage characteristics and activation energy analysis confirm thermally driven dark current increasing with applied field. Impedance spectroscopy reveals the dominant deep trap states within the InAs CQD layer, being tail states of the conduction band that reach down to ∼0.4 eV below the band edge, with a density of ∼2 × 1016 cm-3. The temperature-induced increase in carrier density and reduction in built-in potential within the depleted InAs layer reflect trap filling and Fermi level pinning in the N and P layers. The trapping-detrapping induced noise reduces the specific detectivity (D*) at -1 V by 1.97 orders at 1 Hz and by 1.52 orders of magnitude at 10 Hz relative to the shot-noise-limited baseline. At frequencies ∼ ≥500 Hz the D* approaches the calculated limit of 2.5 × 1011 Jones. Finally, we demonstrate infrared imaging by monolithically integrating the photodiode with a Si read-out IC, enabling imaging beyond the spectral range of CMOS sensors.

We present the fabrication and characterization of capacitive micromachined ultrasound transducers (CMUTs) on glass substrates. The devices exhibit electromechanical coupling efficiency, fractional bandwidth, and transmit sensitivity comparable to state-of-the-art silicon-based CMUTs for an in-water frequency range of 4 - 12 MHz. Performance improves with higher DC bias, though dielectric charging may affect long-term stability. The used process flow is compatible with existing flat-panel display production lines, paving the way for large-area and flexible transducer arrays tailored for continuous ultrasound monitoring in and outside hospitals.

Sensors are integrated into collaborative robot systems to ensure the safety of human workers by allowing them to perceive their environments, detect human presence, and adjust their actions accordingly. This preferred reporting items for systematic reviews and meta-analyses extension for scoping review (PRISMA-ScR) focuses on current sensor-enabled safety systems for human-robot collaboration (HRC) in the manufacturing industry based on both scientific papers and patents. From the initial search of 6669 references, 281 underwent full-text review and segmentation based on the sensor technology, installation location, and safety operating mode according to the ISO/TS 15066 standard. In the last decade, there has been a clear trend of increasing sensor-enabled safety systems. The dominant sensors used are infrared (IR)-structured light, capacitive, light detection and ranging (LiDAR), resistive, stereo/depth camera, RaDAR, and laser scanners. The primary safety operating mode identified was speed and separation monitoring (SSM). Some systems integrate multiple sensor types, with the most common combinations being LiDAR with stereo cameras or LiDAR with capacitive sensors, and laser scanners with RaDAR. We suggest multisensor integration and standardized benchmarks for future development. This review is among the few that employ the PRISMA-P protocol to study sensor technologies and contribute to a more systematic understanding of the current state of the art in this area.

The pull-in and pull-out voltages are important characteristics of Capacitive Micromachined Ultrasound Transducers (CMUTs), marking the transition between conventional and collapse operation regimes. These voltages are commonly determined using capacitance–voltage (C-V) sweeps. By modeling the operating conditions of an LCR meter in COMSOL Multiphysics®, we demonstrate that the measured capacitance comprises both static and dynamic capacitances, with the dynamic capacitance causing the appearance of a peak in the effective C-V curve. Furthermore, Laser Doppler Vibrometer (LDV) measurements and electromechanical simulations indicate the occurrence of collapse–snapback phenomena during the C-V sweeps. This study, through advanced simulations and experimental analyses, demonstrates that the transient membrane behavior significantly affects the apparent capacitance–voltage characteristics of electrostatically actuated Micro-Electromechanical Systems (MEMS).

Colloidal quantum dots (QDs), as a low-cost, flexibly tunable and fabrication scalable semiconductor material, have demonstrated exceptional capabilities in many complex applications including high-quality displays, high-resolution infrared imaging, advanced spectrometry and integration into photonic circuits. This study explores combining the tunable spectral response features of QD-based photodiodes (QDPDs) with dispersive photonic integrated circuits (PICs), demonstrating a spectrometer with operational spectral range extended beyond its original free spectral range (FSR). Experimentally, two types of PbS QDPDs, with different absorption features, were integrated in cascade on the output channels of a planar concave grating (PCG) with a 90 nm FSR. The differential responses of these QDPDs to two adjacent diffraction orders of the PCG enabled the creation of a spectrometer with a spectral range of approximately 180 nm, effectively decoupling two FSRs of the PCG. The proposed cascaded QDPDs, with diverse spectral photodetection capabilities, present great potential when integrated into complex optical systems.

Conventional Capacitive Micromachined Ultrasound Transducers (CMUTs) are generally produced on silicon wafers, limiting the size, form factor, hence applications, of the transducer arrays. In this paper, we unveil a CMUT fabrication technique that can enable the realization of high-density ultrasound arrays on large-area flexible substrates for a variety of new applications in ultrasonic sensing. We also compare optical inspection and electrical characterization methods to measure the pull-in voltage and resonance frequency of the fabricated CMUTs and show that these methods can be used to assess the yield and uniformity of the fabrication process.

In this paper, we present thin-film photodetector (TFPD) image sensors for the short-wave infrared (SWIR) range. Monolithic integration of quantum dot (QD) absorbers enables quantum efficiency of 70% at 1400 nm and pixel pitch below 2 μm. We present image sensors on custom CMOS readout fabricated using 130 nm node. We review latest advancements on the photodiode stack and the pixel engine, including the thin-film pinned photodiode architecture. Furthermore, we study the manufacturing flows to realize full wafer capability for volume processing. QD image sensors are paving the way to add augmented vision into future XR systems with extra functionalities.

Silicon photonics faces a persistent challenge in extending photodetection capabilities beyond the 1.6 µm wavelength range, primarily due to the lack of appropriate epitaxial materials. Colloidal quantum dots present a promising solution here, offering distinct advantages, such as infrared wavelength tunability, cost-effectiveness, and facile deposition. Their unique properties position them as a potential candidate for enabling photodetection in silicon photonics beyond the conventional telecom wavelength, thereby expanding the potential applications and capabilities within this domain. In this study, we have successfully integrated lead sulfide (PbS) colloidal quantum dot photodiodes (QDPDs) onto silicon waveguides using standard process techniques. The integrated photodiodes exhibit a remarkable responsivity of 1.3 A/W (with an external quantum efficiency of 74.8%) at a wavelength of 2.1 µm, a low dark current of only 106 nA, and a bandwidth of 1.1 MHz under a −3 V bias. To demonstrate the scalability of our integration approach, we have developed a compact 8-channel spectrometer incorporating an array of QDPDs. This achievement marks a significant step toward realizing a cost-effective photodetector solution for silicon photonics, particularly tailored for a wide range of sensing applications around the 2 µm wavelength range.

Colloidal quantum dots (CQDs) are cutting-edge optoelectronic semiconductor nanocrystals that enable short-wave infrared (SWIR) vision by a widely tunable SWIR light absorption. Thanks to the advances in CQD surface ligand engineering, SWIR detectors and emitters will soon find their way into products. The CQD-based optoelectronic devices are being optimized by adapting the size of CQDs and selection of the ligands, and yet, the measurement schemes of energy band structure based on different ligands and processes of ligand exchange are not systematically studied. In this work, we systematically characterize the energy band structure of PbS (absorbing at different SWIR wavelengths) and InAs with various ligands for both solid-state and liquid-phase ligand exchange (LPLE) processes [solid-state ligand exchange (SSLE) and LPLE] by using ultraviolet photoelectron spectroscopy. The deduced energy band structures reveal that the apparent energy difference between the Fermi and valence band maximum, |E F - E VBM|, largely depends on the physical density and distribution of the CQDs within the probing area. Transmission electron microscopy images, X-ray photoelectron spectroscopy, atomic force microscopy, and variable angle spectroscopic ellipsometry reveal details of the CQD distribution, surface elemental profile, and topologies and how they affect the observed energy band structure. We demonstrate that the multistep coating improves the CQD distribution and packing density, resulting in more reliable and reproducible results that represent the bulk CQD film energy band structure. The comparison of solid and liquid phase ligand-exchanged PbS and InAs SWIR CDQs energetics indicates that the LPLE ensures more uniform dispersion and a high packing density of CQDs regardless of the solution concentration. The photoemission-deduced energy band structures are validated by fabricating thin-film photodiodes using SWIR SSLE PbS and LPLE In(As,P) CQDs. The Fermi-referenced band structures of the fabricated full photodiode stacks including band offsets and bending are discussed to improve our understanding of the device working principles and to further optimize the devices.

Microheaters have evolved to become a key component of devices in a wide range of applications, many of which require a thermal profile with good uniformity. To this end, it is critical not only to select an appropriate device geometry but also to have reliable tools to assess the uniformity in the microscale. This paper presents a collection of novel sensors to experimentally extract the mean temperature in various regions of the micro-hotplate with high accuracy, offering an innovative alternative to other uniformity measurement tools that are often not available or not sufficiently precise. The studies are articulated around a series of meander-based microheaters, for which the temperature versus voltage profile, response time, power consumption and uniformity are studied. In this way, insight into the influence of different geometrical parameters (i.e. line arrangement, scaling, linewidth and line spacing) is provided. Finite Element Method simulations are performed based on certain assumptions and boundary conditions and exhibit strong concordance with our experimental data, thus we demonstrated that the sensors serve as a tool to validate the representativeness of a model. 2024-0110

Image sensors are must-have components of most consumer electronics devices. They enable portable camera systems, which find their way into billions of devices annually. Such high volumes are possible thanks to the complementary metal-oxide semiconductor (CMOS) platform, leveraging wafer-scale manufacturing. Silicon photodiodes, at the core of CMOS image sensors, are perfectly suited to replicate human vision. Thin-film absorbers are an alternative family of photoactive materials, distinguished by the layer thickness comparable with or smaller than the wavelength of interest. They allow design of imagers with functionalities beyond Si-based sensors, such as transparency or detectivity at wavelengths above Si cutoff (e.g., short-wave infrared). Thin-film image sensors are an emerging device category. While intensive research is ongoing to achieve sufficient performance of thin-film photodetectors, to our best knowledge, there have been few complete studies on their integration into advanced systems. In this paper, we will describe several types of image sensors being developed at imec, based on organic, quantum dot, and perovskite photodiode and show their figures of merit. We also discuss the methodology for selecting the most appropriate sensor architecture (integration with thin-film transistor or CMOS). Application examples based on imec proof-of-concept sensors are demonstrated to showcase emerging use cases.

We report a high-speed low dark current near-infrared (NIR) organic photodetector (OPD) on a silicon substrate with amorphous indium gallium zinc oxide (a-IGZO) as the electron transport layer (ETL). In-depth understanding of the origin of dark current is obtained using an elaborate set of characterization techniques, including temperature-dependent current-voltage measurements, current-based deep-level transient spectroscopy (Q-DLTS), and transient photovoltage decay measurements. These characterization results are complemented by energy band structures deduced from ultraviolet photoelectron spectroscopy. The presence of trap states and a strong dependency of activation energy on the applied reverse bias voltage point to a dark current mechanism based on trap-assisted field-enhanced thermal emission (Poole-Frenkel emission). We significantly reduce this emission by introducing a thin interfacial layer between the donor: acceptor blend and the a-IGZO ETL and obtain a dark current as low as 125 pA/cm2 at an applied reverse bias of -1 V. Thanks to the use of high-mobility metal-oxide transport layers, a fast photo response time of 639 ns (rise) and 1497 ns (fall) is achieved, which, to the best of our knowledge, is among the fastest reported for NIR OPDs. Finally, we present an imager integrating the NIR OPD on a complementary metal oxide semiconductor read-out circuit, demonstrating the significance of the improved dark current characteristics in capturing high-quality sample images with this technology.

Sensors based on quantum dot photodiodes promise quality and accessibility improvement of infrared imaging. We demonstrate miniaturization by sub-2-mu m pixel pitch arrays. Functionality is confirmed with external quantum efficiencies above 40% at 1450 nm. Monolithic integration enables high throughput and wide deployment of short-wave infrared (SWIR) imagers in applications that previously could not afford them.

Image sensors made using silicon complementary metal–oxide–semiconductor technology can be found in numerous electronic devices and typically rely on pinned photodiode structures. Photodiodes based on thin films can have a high absorption coefficient and a wider wavelength range than silicon devices. However, their use in image sensors has been limited by high kTC noise, dark current and image lag. Here we show that thin-film-based image sensors with a pinned photodiode structure can have comparable noise performance to a silicon pinned photodiode pixel. We integrate either a visible-to-near-infrared organic photodiode or a short-wave infrared colloidal quantum dot photodiode with a thin-film transistor and silicon readout circuitry. The thin-film pinned photodiode structures exhibit low kTC noise, suppressed dark current, high full-well capacity and high electron-to-voltage conversion gain, as well as preserving the benefits of the thin-film materials. An image sensor based on the organic absorber has a quantum efficiency of 54% at 940 nm and read noise of 6.1e – .

We present a thin‐film piezoelectric micromachined ultrasonic transducer (PMUT) technology compatible with flat‐panel manufacturing methods. Using the developed flow which is based on a low temperature AlScN piezoelectric layer, we fabricate large area 48x48 element PMUT arrays on glass. Beam steering and ultrasound medical imaging are demonstrated. The developed transducer technology can be combined with a TFT backplane and has the potential of direct integration on top of display size glass sheets, expanding the boundaries of ultrasound application domains.

Thin-film photodiodes (TFPD) monolithically integrated on the Si Read-Out Integrated Circuitry (ROIC) are promising imaging platforms when beyond-silicon optoelectronic properties are required. Although TFPD device performance has improved significantly, the pixel development has been limited in terms of noise characteristics compared to the Si-based image sensors. Here, a thin-film-based pinned photodiode (TF-PPD) structure is presented, showing reduced kTC noise and dark current, accompanied with a high conversion gain (CG). Indium-gallium-zinc oxide (IGZO) thin-film transistors and quantum dot photodiodes are integrated sequentially on the Si ROIC in a fully monolithic scheme with the introduction of photogate (PG) to achieve PPD operation. This PG brings not only a low noise performance, but also a high full well capacity (FWC) coming from the large capacitance of its metal-oxide-semiconductor (MOS). Hence, the FWC of the pixel is boosted up to 1.37 Me- with a 5 μm pixel pitch, which is 8.3 times larger than the FWC that the TFPD junction capacitor can store. This large FWC, along with the inherent low noise characteristics of the TF-PPD, leads to the three-digit dynamic range (DR) of 100.2 dB. Unlike a Si-based PG pixel, dark current contribution from the depleted semiconductor interfaces is limited, thanks to the wide energy band gap of the IGZO channel material used in this work. We expect that this novel 4 T pixel architecture can accelerate the deployment of monolithic TFPD imaging technology, as it has worked for CMOS Image sensors (CIS).