Kyriaki Minoglou

10 µm pixel-to-pixel pitch hybrid backside illuminated AlGaN-on-Si imagers for solar blind EUV radiation detection

We present the first measurement results from hybrid AlGaN-on-Si-based Extreme Ultraviolet (EUV) imagers with 10 µm pixel-to-pixel pitch. The 256×256 backside illuminated Focal Plane Arrays (FPAs) were hybridized to dedicated Si-based CMOS Readouts (ROICs). The AlGaN active layer with 40% Al concentration provides an intrinsic rejection of wavelengths larger than 280 nm (solar blindness), together with enhanced radiation hardness (1). Sensitivity in Deep UV (DUV), Far UV (FUV) and Extreme UV (EUV) was verified using synchrotron radiation down to a wavelength of 1 nm.

Backside-Illuminated GaN-on-Si Schottky Photodiodes for UV Radiation Detection

In this letter, we report on the fabrication of near-ultraviolet photodetectors based on gallium nitride (GaN) layers grown on a Si(111) substrate. Optoelectronic characterization was performed using front-side and backside illumination, the latter possible by locally etching the Si substrate under the detectors using reactive ion etching. The dark current after removal of the Si substrate decreased by two orders of magnitude to around 20 fA at -1 V for a 300-mum-diameter Schottky photodiode. Responsivity at the cutoff wavelength (370 nm) was equal to 35 mA/W for the backside illumination. Detection at smaller wavelengths was not possible due to a nonoptimized layer stack. These first results do however illustrate the potential of backside-illuminated GaN-on-Si Schottky photodiodes in 2-D UV imagers.

Reduction of Electrical Crosstalk in Hybrid Backside Illuminated CMOS Imagers using Deep Trench Isolation

Hybrid backside illuminated CMOS imagers with zero pixel-to-pixel electrical crosstalk were developed. The application of highly doped polysilicon filled high aspect ratio trenches between pixels to reduce crosstalk is unique. These 1¿m wide 50¿m deep trenches enforce a lateral drift field between pixels, which counteracts diffusion and drastically reduces electrical crosstalk. Quantitative crosstalk characterization of trenched and non-trenched imagers is presented.

AlGaN-on-Si-Based 10-

We report on the fabrication of extreme ultraviolet (EUV) hybrid imagers with backside-illuminated detector chip based on aluminum gallium nitride (AlGaN) layers grown on silicon and integrated with CMOS readout chip. The focal plane array (FPA) size is 256 × 256 pixels with 10-μm pixel-to-pixel pitch. The devices were characterized at wavelengths from 300 down to 1 nm using synchrotron radiation. An upper cutoff wavelength of 280 nm was observed, as expected from the AlGaN active layer composition (40% Al). Thus, the imagers have a high rejection ratio of the near UV and visible radiation. Moreover, no degradation due to proton irradiation was observed for 60-MeV energy and 5 ·1010 protons/cm2 dose. Furthermore, devices with thin silicon substrate layer that is intentionally left were fabricated, and response only in the EUV range was observed. These results demonstrate the possibility of achieving high-resolution EUV imaging with AlGaN-based FPAs, which is very promising for high-end industrial, scientific, and space applications.

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This paper presents two aspects of ongoing research at Imec, to develop high-end CMOS APS sensors, optimized for space-born imaging. Both hybrid and monolithic thinned backside illuminated CMOS imagers with a unique combination of techniques and performance enhancing concepts have been developed. Here we report on their radiation tolerance and UV sensitivity, two critical characteristics for space science imaging instruments. Radiation testing, using both proton and gamma irradiation, of CMOS imagers proved that dark current performance did not significantly deteriorate. Also, initial test images taken under 185-400 nm illumination, showed the imagers to be UV sensitive.

Pixel-to-Pixel Pitch Hybrid Imagers for the EUV Range

This paper presents a new imager platform developed at imec enabling the monolithic integration of 130 nm CMOS image sensors (CMOS/CIS) with charge coupled devices (CCD). The process module was successfully developed and the potential of this embedded CCD in CMOS (eCCD) was demonstrated with the fabrication of a time delay integration (TDI) imager.

Backside illuminated thinned CMOS image sensors for space imaging

One key challenge in the development of backside-illuminated CMOS imagers is to keep crosstalk (XT) low while enabling high quantum efficiency (QE). In this paper, the tradeoff between XT and QE is optimized and demonstrated in two ways. First, a novel optimized two-step graded EPI was developed and implemented, giving excellent QE and XT data. Second, in other imagers, pixel-separating trenches were employed to eliminate XT, although at the cost of reduced QE × fill factor. Finally, to accurately evaluate the XT performance, an innovative on-chip slanted light shield was implemented on the imager array periphery, eliminating the need for a complex XT characterization setup.

Enhanced time delay integration imaging using embedded CCD in CMOS technology

Backside-illuminated (BSI) imagers are becoming popular due to their enhanced light sensitivity. During their fabrication advanced Si wafer thinning is used in combination with backside surface passivation techniques. In this section both technology for thin (hybrid) backside-illuminated imagers as well as the trade-offs they present between quantum efficiency and crosstalk are discussed and illustrated, with the use of imec imager results.

First Demonstration of Hybrid CMOS Imagers With Simultaneous Very Low Crosstalk and High-Broadband Quantum Efficiency

This paper introduces a novel imaging spectrometer subsystem concept, the Smart Slit Assembly (SSA), that improves instrument performances and enables new features for future Earth Observation. Derived from CarbonSat (ESA study) requirements, a concept of an SSA based on MEMS micro-shutters/mirrors and associated instrument design aspects are presented. The SSA replaces the classical grating spectrometer slit aperture in the focal plane of the telescope with three core elements, namely an input multimode waveguide array followed by a spatial light modulator (SLM) and an output multimode waveguide array which ends at the slit aperture viewed by the spectrometer. The SLM’s in-and-outputs being coupled to waveguide arrays leads to an enhanced SLM with light de-coherence, polarization scrambling and scene/object homogenization capabilities. The additional advantage of this subsystem’s arrangement is that waveguide level homogeneous spatial light modulation can be achieved with spatially in-homogeneous coupling from in to output multimode waveguides, allowing new, simpler and less costly designs for the SLM part of the SSA. The SSA is particularly useful for instance to reduce stray light by scene/object selection or modulation (e.g. de-clouding, intensity equalization), relax on the required dynamic range of the detectors, increase spectral stability by waveguide level intensity homogenization/scrambling, continuous in-flight monitoring of the co-registration between two or several spectrometer channels and inflight monitoring of stray light.

Thinned Backside-Illuminated (BSI) Imagers

The European Space Agency has a very strong interest in the performance enhancement of detector arrays for future scientific and astronomy missions. Improvements in Visible and Infrared wavelengths are of particular interest and the Agency undertakes a programme of continuous development aimed at enhancing the capability of detectors in these wavebands. This paper presents the status of these detector technology development activities.