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In this letter, we present a small pixel pitch image sensor optimized for high external quantum efficiency in short-wavelength infrared (SWIR). Thin-film photodiodes based on PbS colloidal quantum dot (CQD) absorber allow us to exceed the spectral limitations of silicon’s absorption while maintaining the benefits of CMOS technology. By monolithically integrating PbS CDQ thin films with CMOS readout arrays, high-pixel density SWIR image sensors can be achieved. To overcome the remaining disadvantages of the CQD-based image sensors over their bulk III-V semiconductor counterparts (lower sensitivity and reduced linearity), the thin-film photodiode stack is adapted towards the used readout circuit. A prototype image sensor with a $768\times 512$ resolution of 5- $\mu \text{m}$ pitch pixels is fabricated by using a modified 130 nm CMOS process for readout IC, together with the new CQD thin-film photodiode on top. Thanks to the optimized photodiode stack and co-integration process, the prototype image sensor shows less than 5% linearity error while having 40% external quantum efficiency in SWIR, which enables acquisition of high-quality images.

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.

In an effort to fabricate In–Ga–Zn oxide (IGZO) thin-film transistors (TFTs) that combine high performance and high stability, we optimize sputtering conditions to create devices based on different...

A flexible PMUT device which can be applied on curved surfaces is presented. The oscillation behavior of the device under different curvatures (from ${\kappa } = 0$ to ${\kappa } =20\,\,\text{m}^{\mathbf {-1}}$ ), shows both modal frequency and vibration velocity shifts. The impact of bending of the device is discussed, in terms of stress given to the diaphragm. When the device is curved, additional stress is added to the diaphragm, opposite to the process-originated stress already presents on the device. An analytical model is introduced that explains the mechanical boundary condition of the diaphragm, which is altered when the device is laminated on a curved surface. The model can predict driving frequency and optimum design of the device according to the bending curvature. When the device is bent with a curvature of $\boldsymbol {\kappa } =20\,\,\text{m}^{\mathbf {-1}}$ , a driving frequency shift of around 10 kHz, which is 2% of the center frequency (503kHz) is predicted as well as measured, compared to device on the flat surface. The oscillation performance of the device increases by 37%, following the prediction of the model. [2020-0348]

Colloidal quantum dots based on lead sulfide (PbS) are very attractive materials for the realization of novel image sensors. They offer low cost synthesis, compatibility with a variety of substrates and processing on large area. The tunable band gap enables selective light detection from the visible wavelengths up to the short-wave-infrared (SWIR). This work describes the roadmap towards the integration of quantum dot photodiodes (QDPD) on top of a Si based CMOS read-out circuit. Photodiodes using an n-p junction architecture are fabricated on Si substrates, showing a dark current of 30 nA/cm2 at −1 V reverse bias, EQE above 20% and specific detectivity above 1012 cm Hz1/2 W−1 at the wavelength of 940 nm. Efficiency is improved by reducing absorption in the top contact through optical design. Furthermore, photolithographic patterning of the thin-film stack is introduced for the first time, showing the feasibility of pixel pitches down to $40~\mu \text{m}$ , opening the way towards high resolution monolithic infrared imagers and the incorporation of infrared and visible sensitive pixels side by side.

ispartof: ADVANCED OPTICAL MATERIALS vol:9 issue:24 status: published

In this work, we present a photodetector based on PbS colloidal quantum dots which can be used for low-cost, high-resolution multispectral imaging in the short-wavelength infrared range. Using versatile solution-based processing of thin films, we fabricated a switchable, dual-channel, two-terminal photodetector that can be monolithically integrated with small-pitch CMOS readout arrays. Its vertically stacked structure provides higher spatial resolution compared to conventional snapshot multispectral image sensors. We show the results of the optical simulations based on the transfer matrix method, which allowed us to achieve a wavelength-tunable narrowband response. We demonstrate the operation of the photodetector and its facile tunability by showing an EQE of more than 25% at different bands in the wavelength range of 1-1.5 μm. This work demonstrates the potential of the emerging thin-film technology for multispectral imaging.

Device optimization of light-emitting diodes targets the most efficient conversion of electrically injected charges into emitted light. Where charges recombine and where light is emitted from is known as the emission zone. Determining its form is key to better understanding the physical processes determining device performance. However, a thorough measurement study has not been shown. Here we present an accessible technique to visualize the emission zone in unprecedented detail at all luminescing current densities. Only a single emission spectrum must be measured (at normal direction to the device layers with no additional optics) and compared with the simulated emission spectrum. This method allows physical understanding based, instead of speculative, optimisation of LED device architectures. We demonstrate its impact by examining the device structure – emission zone – lifetime relationships of a thermally activated delayed fluorescence OLED to achieve an ultralong 4500 hour T95 lifetime at 1000 cd/m2 with 20% external quantum efficiency.

In this study, two different semiconductor-grade polymers are utilized to build up membrane-based electromechanical transducers. With three to four orders of magnitude lower modulus in comparison with silicon, the use of polymers as the vibrating membrane improves the mechanical output characteristics where larger vibration amplitude is needed. Novel processing methods, including an excimer laser-aided wafer-to-water transferring technique, have been developed for the introduction of polymers into the standard cleanroom fabrication environment. Both piezoelectric and electrostatic transducers are fabricated on glass substrates and then characterized with laser dropper velocimetry. Comparison is made to exemplify the advantages and disadvantages of using polymers with varied dynamic specifications for different applications, where the compromise between fabrication robustness and device performance is needed.