To ensure the mechanical strength of the cells in shaped photovoltaic modules, it is important to know their double bending radius limit, as well as their mechanical breaking limits. This study focuses on the mechanical characterization of Si cells under double curvature load. It aims at determining the mechanical limits of silicon under double curvature, as well as the minimum radii of curvature reachable without breaking the cell. A numerical model representing the curvature of a cell in a double-curvature wedge has been implemented. It aims at predicting, for a given cell thickness, the acceptable double radius limit. This numerical model is validated with experimental tests to quantify the mechanical limits of silicon under double curvature. Experimental tests were performed on different types of cells -wafers, cells with or without interconnections- to evaluate the impact of each process step on the mechanical strength of cells under this double curvature load.

Curved image sensors, not having to correct the field curvature, are considered a relevant solution for improving the vast majority of optical systems. They offer the possibility of designing compact aberration-free optical systems. In this work, we explain the advantage of the curved sensor system using the aberration theory. A complete procedure was developed to produce functional curved sensors and functional prototypes were carried out. This paper focuses on the tolerancing process of curved sensors and its inclusion in optical design. A compact objective prototype designed and produced demonstrates the advantage of curvature and the impact of tolerancing.

We review the main challenges for fabricating high performance microLED displays for direct view applications from watch to large area TV. The main one is the transfer process of the microLEDs on the large area TFT backplane. We show how the microtube technology developed at LETI can ensure in one step both the mechanical and electrical connection between the two parts. Driving electronics is also a strong challenge. We also report a new approach providing full CMOS driving of the MicroLED display and a more efficient transfer solution. This new approach is paving the way for high-performance MicroLED displays, and in a much wider range of applications

We discuss the main challenges for the fabrication of emerging microLED displays. We shown that microtube technology is very well adapted to these new kind of displays, since it provides both mechanical and electrical connection of the microLEDs on the receiving substrate. Also, we present a new fabrication approach, where an elementary unit consists of all‐in‐one‐ RBG MicroLEDs on CMOS driving circuit.

Due to the increasing dimension, complexity, and cost of future astronomical surveys, new technologies enabling more compact and simpler systems are required. The development of curved detectors allows enhancement of the performances of the optical system used (telescope or astronomical instrument), while keeping the system more compact. We describe here a set of five curved complementary metal-oxide semiconductor (CMOS) detectors developed within a collaboration between CEA-LETI and CNRS-LAM. These fully functional detectors 20 Mpix (CMOSIS CMV20000) have been curved to different radii of curvature and spherical shapes (both convex and concave) over a size of 24×32  mm2. Before being able to use them for astronomical observations, we assess the impact of the curving process on their performances. We perform a full electro-optical characterization of the curved detectors, by measuring the gain, the full well capacity, the dynamic range, and the noise properties, such as dark current, readout noise, pixel-relative non-uniformity. We repeat the same process for the flat version of the same CMOS sensor, as a reference for comparison. We find no significant difference among most of the characterization values of the curved and flat samples. We obtain values of readout noise of 10e- for the curved samples compared to the 11e- of the flat sample, which provides slightly larger dynamic ranges for the curved detectors. Additionally, we measure consistently smaller values of dark current compared to the flat CMOS sensor. The curving process for the prototypes shown in this paper does not significantly impact the performances of the detectors. These results represent the first step toward their astronomical implementation.

Curved sensors is a well-adapted technology solution to enhance the vast majority of optical systems. It helps to remove lenses and simplify optical architectures. These advantages open news challenges such as a specific fabrication process applied to curved sensors and new rules for final system integration. In this paper, we first introduce benefits of curved sensors applied on a compact high-resolution camera to define the sensor shape specifications and to reach high performances and compactness (-50% compared to a benchmark system). Mechanical limits and optical modeling are used. Then, based on these curved specifications, a novel collective curving process is described, developed on 1/1.8" format CMOS image sensors with a radius or curvature target R= 55 mm and R=60 mm. This work includes packaging and assembly steps, optimizations, and morphological characterizations in accordance to optical design requirements. Finally, a dedicated optical test bench is used for Modulation Transfer Function (MTF) characterization of the final camera prototype. All these experiments and optical results introduce new opto-mechanical requirements and demonstrate the feasibility and high performances of systems with curved sensors.

We have fabricated blue and green microLED display prototypes. The microLEDs have been transferred using microtube technology. The interest of microtube for large area microLED displays has been demonstrated by providing both mechanical and electrical connection. Overall, this technology brings a lot of advantages compared to existing solutions.

Curved sensors are a suitable technological solution to enhance the vast majority of optical systems. In this work, we show the entire process to create curved sensor-based optical systems and the possibilities they offer. This paper defines the boundaries of the reachable curvatures for a full range of monolithic sensors. We discuss how the curved focal plane shape is related to the imaged scenes and optical parameters. Two camera prototypes are designed, realized, and tested, demonstrating a new compact optical architecture for a 40 deg compact objective as well as a wide-field fisheye zoom objective using a convex sensor to image a 180 deg field of view.

Many are the optical designs that generate curved focal planes for which field flattener must be implemented. This generally implies the use of more optical elements and a consequent loss of throughput and performances. With the recent development of curved sensor this can be avoided. This new technology has been gathering more and more attention from a very broad community, as the potential applications are multiple: from low-cost commercial to high impact scientific systems, to mass-market and on board cameras, defense and security, and astronomical community. We describe here the first concave curved CMOS detector developed within a collaboration between CNRS-LAM and CEA-LETI. This fully-functional detector 20 Mpix (CMOSIS CMV20000) has been curved down to a radius of R-c =150 mm over a size of 24x32 mm(2). We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the flat version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor.

Many astronomical optical systems have the disadvantage of generating curved focal planes requiring flattening optical elements to project the corrected image on flat detectors. The use of these designs in combination with a classical flat sensor implies an overall degradation of throughput and system performances to obtain the proper corrected image. With the recent development of curved sensor this can be avoided. This new technology has been gathering more and more attention from a very broad community, as the potential applications are multiple: from low-cost commercial to high impact scientific systems, to mass-market and on board cameras, defense and security, and astronomical community. We describe here the first concave curved CMOS detector developed within a collaboration between CNRS-LAM and CEA-LETI. This fully-functional detector 20 Mpix (CMOSIS CMV20000) has been curved down to a radius of R-c = 150 mm over a size of 24x32 mm(2). We present here the methodology adopted for its characterization and describe in detail all the results obtained. We also discuss the main components of noise, such as the readout noise, the fixed pattern noise and the dark current. Finally we provide a comparison with the flat version of the same sensor in order to establish the impact of the curving process on the main characteristics of the sensor.

Over the recent years, a huge interest has grown for curved electronics, particularly for opto-electronics systems. Curved sensors help the correction of off-axis aberrations, such as Petzval Field Curvature, astigmatism, and bring significant optical and size benefits for imaging systems. In this paper, we first describe advantages of curved sensor and associated packaging process applied on a 1/1.8'' format 1.3Mpx global shutter CMOS sensor (Teledyne EV76C560) into its standard ceramic package with a spherical radius of curvature Rc=65mm and 55mm. The mechanical limits of the die are discussed (Finite Element Modelling and experimental), and electro-optical performances are investigated. Then, based on the monocentric optical architecture, we proposed a new design, compact and with a high resolution, developed specifically for a curved image sensor including optical optimization, tolerances, assembly and optical tests. Finally, a functional prototype is presented through a benchmark approach and compared to an existing standard optical system with same performances and a x2.5 reduction of length. The finality of this work was a functional prototype demonstration on the CEA-LETI during Photonics West 2018 conference. All these experiments and optical results demonstrate the feasibility and high performances of systems with curved sensors.

Optical designs generate curved focal planes for which field flatteners must be implemented. A field flattener consists of an additional lenses block with a consequent loss of throughput and performances. With the recent packaging development for curved sensors, this can be omitted and the optical system simplified. In this paper, we first describe advantages of curved sensors and associated packaging process fabrication, applied on a full-frame format 20Mpx global shutter CMOS image sensor (AMS CMV20000 product). Mechanical limits for curving such full-frame sensor type are discussed, using Finite Element Modelling to manage die breaks. We have curved sensors with a spherical shape from concave Rc=150mm to convex Rc=280mm. We packaged them into their ceramic package and we carried out electro-optical characterization, in collaboration with the AMS CIS characterization team. The electro-optical performances of the curved sensors are investigated and the results compared to the datasheet. We mainly focus on response uniformity, dark noise and dark current results. We present those characteristics in the form of mappings in order to investigate any impact of curvature process on image sensor performances. All these experiments and their electro-optical results demonstrate the feasibility of curving full-frame image sensor with only small electro-optical parameter shift compared to a typical flat reference.

Since few years, there has been an increasing interest and demand in flexible electronics. Standard imaging system consists of an optical module (set of lenses) and an image sensor. For wide field of view applications, and due to the curved shape of lenses and mirrors, the flat image after being propagated through the optical system is not flat but curved, i.e. the off-axis light focuses in a curved manner. This problem is called Petzval Field Curvature Aberration (Petzval FCA). It is generally fixed by additional complex lenses to “flatten” the image plane. We propose another approach with a hemispherical curved sensor technology. It allows eliminating FCA directly at the sensor level and thus makes it possible to drastically simplify, and hence miniaturize, the optical system architecture. First, a brief state of the art on curved detectors will be detailed for different application fields. Bendable capacities of hydrid detectors (included interconnection layer) were fully investigated and tested in the past [1, 2]. Moreover, a hemi-spherically curved visible image sensor with better optical characteristics (image quality) was realized and patented by Sony Company in 2014 [3]. Recently, a tunable curving packaging technology, with new optical functions possibilities has been presented in Electronic Component and Technology Conference 2016 [4]. Then, CEA-LETI curving technologies will be explained to address fixed and tunable curvature packaging applications, included modeling and technical process steps. Characterization of curved sensors prototypes have been performed to understand mechanical and electro-optical bending limits and will be also presented in the paper. Based on an existing fisheye flat sensor optical design, a curved focal plane will be described, showing that it's possible to simplify the standard system from 14 lenses (11 types of optical glass) with 2 aspheric lenses, to only 9 lenses (−35%), 3 types of optical glasses, without aspheric surfaces. The benefits of a curved sensor will be summarized into two categories: those related to the optical system design and those related to the quality of images produced by a camera with curved sensor. Optical system:» Miniaturization of optical devices (volume, weight);» Simplification of the lenses alignment process (due to reduced number of lenses);» Suppression of aspheric lenses;» Wide field of view enhancement. Image quality:» More homogeneous image quality (reduced image noise);» Similar or improved resolution and higher sensitivity;» Corrected distortion occurring along the image edges. Finally, curved CMOS image sensor roadmaps and perspectives will be discussed: from a market point of view, application field surveys have been done on mass market applications (mobile, consumer…), photography, automotive… From a technical aspect, a curving technologies roadmap will be proposed, leaded by applications needs, on single chip, collective, and wafer level processes.

Over the recent years, a huge interest has grown for curved electronics, particularly for opto-electronics systems. Indeed, curved sensors help the correction of off-axis aberrations, such as Petzval Field Curvature and astigmatism. In this paper, we describe benefits of curvature and tunable curvature on an existing fish-eye lens. We proposed a new design architecture, compact and with a high resolution, developed specifically for a curved image sensor. We discuss about aberrations and effect of higher sensor curvature on third order aberrations. Besides, we show results of sensors' mechanical limits and its electro-optical characterization. Finally, all these experiments and optical results demonstrate the feasibility and high performances of systems with curved sensors.

We present high performance imagers based on our current know-how in curved detectors manufacturing for VIS or NIR applications. These extremely compact systems are preparing the future of curved imagery.

In this paper, our latest developments on high vacuum packaging technology at the wafer level are presented. The main objective of our works has been to demonstrate the feasibility of hermetic high vacuum wafer level packaging of MEMS (vacuum target is 10 -3 to 10 -4 mbar) using either anodic or eutectic bonding (AuSi). In the frame of this work, a test vehicle based on a MEMS resonator is used to characterize the vacuum inside the packaging by measuring the Quality factor (Q factor) of the resonator. The resonator is fabricated using 200 mm BSOI wafers. For capping, either 200 mm glass wafer or 200 mm silicon wafer are used depending on the bonding technology chosen. A deep cavity is created in the cap wafer. A getter is deposited inside the cavity to maintain a high vacuum level after bonding. The wafers are then bonded together using anodic or eutectic bonding and electrical interconnections (TSV) are finally carried out. First, the calibration curve i.e., Q Factor vs residual pressure has been achieved using our resonator with a non-hermetic package and a specific vacuum chamber that allowed us to measure the Q factor of the resonator at different residuals pressures (from 10 -1 to 10 -5 mbar). Then, anodic and eutectic bonding processes have been developed and optimized in order to reach vacuum level as low as 10 -3 mbar after interconnection. In the case of anodic bonding, it turned out that the main issue that has to be addressed was the permeation of noble gas through the glass wafer during interconnection process. For eutectic bonding, outgassing turned out to be the more significant parameter to control. Finally, residual pressure down to 10 -4 mbar has been achieved.

The main objective of this work has been to demonstrate the feasibility of combining hermetic high vacuum level MEMS packaging (vacuum target is below 10(-2) mbar) with 3D feed trough interconnections on 200 mm wafers.A vacuum Wafer Level Packaging (WLP) solution for MEMS will be presented. This solution is assessed on a test vehicle based on a MEMS resonator processed in a silicon wafer hermetically sealed to a glass wafer by an anodic bonding process. The resonator is used to characterize the vacuum inside the packaging by measuring the Quality factor of the resonator (Q factor).At first, a Through Glass Via (TGV) technology has been used. Thanks to this technology the MEMS can be electrically connected to the ASIC by wire bonding through the front side of the assembly.Then, a Through Silicon Via (TSV) solution has been developed through the backside of the assembly that makes possible to directly connect the MEMS to the PCB by flip-chip bonding. Both technologies will be described in this paper.A specific measurement method of the Q factor through the glass has been developed using classical optical microscopy. This allows following the Q factor evolution during TSV process. The Q factor is also determined by electrical tests measurement at wafer level and chip level at the end of the process flow.

For several kinds of MEMS (gyrometers, accelerometers, RF MEMS, bolometers, vacuum allows a significant improvement of performances. Leti has developed a high performance sensor operating at a pressure lower than 10-3 mbar. In a first phase, a ceramic vacuum packaging has been developed: the device is encapsulated in a cavity containing a getter. However, this technique increases considerably the fabrication costs, because it is made at the chip level. For that reason, Leti has also developed wafer-level vacuum packaging process. The process to manufacture encapsulated devices is presented in this paper. The vacuum function is obtained thanks to an additional wafer (glass or silicon wafer), which supports getters. This wafer is bonded by an hermetic bonding. Characterisation of different kinds of bonding, in term of hermeticity, is presented. First chips manufactured with this process have been tested. The vacuum level in the cavities has been measured, and was lower than 10-3 mbar. Moreover, vacuum evolution during 6 months does not show pressure increase. This process can be easily adapted to several MEMS applications. With these experiments, Leti has so proved the possibility of manufacturing low cost vacuum packaged MEMS.