There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Recent developments in color filtering and display technologies have focused predominantly on high resolution, color vibrancy, high efficiency, and slim dimensions. To achieve these goals, metallic nanostructures have attracted extensive research interest due to their abilities to manipulate the properties of light through surface plasmon resonances. In this paper, we review recent representative developments in plasmonic color engineering at the nanoscale using subwavelength nanostructures, demonstrating their great potential in high-resolution and high-fidelity color rendering, spectral filtering applications, holography, three-dimensional stereoscopic imaging, etc.

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Color generation via subwavelength plasmonic nanostructures

A wide dynamic range CMOS image sensor with a burst readout multiple exposure method is proposed. In this method, maximally four different exposure-time signals are read out in one frame. To achieve the high-speed readout, a compact cyclic analog-to-digital converter (ADC) with noise canceling function is proposed and arrays of the cyclic ADCs are integrated at the column. A prototype wide dynamic range CMOS image sensor has been developed with 0.25-/spl mu/m 1-poly 4-metal CMOS image sensor technology. The dynamic range is expanded maximally by a factor of 1791 compared to the case of single exposure. The dynamic range is measured to be 19.8 bit or 119 dB. The 12-bit ADC integrated at the column of the CMOS image sensor has DNL of +0.2/-0.8 LSB.

A wide dynamic range CMOS image sensor with multiple exposure-time signal outputs and 12-bit column-parallel cyclic A/D converters

We report on the design and characterization of a novel time-resolved image sensor fabricated in a 130 nm CMOS process. Each pixel within the 3232 pixel array contains a low-noise single-photon detector and a high-precision time-to-digital converter (TDC). The 10-bit TDC exhibits a timing resolution of 119 ps with a timing uniformity across the entire array of less than 2 LSBs. The differential non-linearity (DNL) and integral non-linearity (INL) were measured at ±0.4 and ±1.2 LSBs, respectively. The pixel array was fabricated with a pitch of 50 μm in both directions and with a total TDC area of less than 2000 μm2. The target application for this sensor is time-resolved imaging, in particular fluorescence lifetime imaging microscopy and 3D imaging. The characterization shows the suitability of the proposed sensor technology for these applications.

A Time-Resolved, Low-Noise Single-Photon Image Sensor Fabricated in Deep-Submicron CMOS Technology

Chromatic devices such as flat panel displays could, in principle, be substantially improved by incorporating aluminum plasmonic nanostructures instead of conventional chromophores that are susceptible to photobleaching. In nanostructure form, aluminum is capable of producing colors that span the visible region of the spectrum while contributing exceptional robustness, low cost, and streamlined manufacturability compatible with semiconductor manufacturing technology. However, individual aluminum nanostructures alone lack the vivid chromaticity of currently available chromophores because of the strong damping of the aluminum plasmon resonance in the visible region of the spectrum. In recent work, we showed that pixels formed by periodic arrays of Al nanostructures yield far more vivid coloration than the individual nanostructures. This progress was achieved by exploiting far-field diffractive coupling, which significantly suppresses the scattering response on the long-wavelength side of plasmonic pixel res...

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High Chromaticity Aluminum Plasmonic Pixels for Active Liquid Crystal Displays

A color image was taken with a CMOS image sensor without any infrared cut-off filter, using red, green and blue metal/dielectric filters arranged in Bayer pattern with 1.75µm pixel pitch. The three colors were obtained by a thickness variation of only two layers in the 7-layer stack, with a technological process including four photolithography levels. The thickness of the filter stack was only half of the traditional color resists, potentially enabling a reduction of optical crosstalk for smaller pixels. Both color errors and signal to noise ratio derived from optimized spectral responses are expected to be similar to color resists associated with infrared filter.

Color filters including infrared cut-off integrated on CMOS image sensor.

An innovative process development for sub-2μm CMOS imager sensors is described, leading to tremendous improvements on main pixel parameters like conversion gain, saturation charge, sensitivity, dark current and noise. A full 3MP demonstrator with 1.75μm pixel pitch and 1.45μm pixel pitch have been successfully designed, fabricated and characterized.

Fully Optimized Cu based process with dedicated cavity etch for 1.75μm and 1.45μm pixel pitch CMOS Image Sensors

A 30 frames/s SXGA 5.6 /spl mu/m pinned photodiode pixel column parallel CMOS image sensor achieves 340 /spl mu/V noise floor and 40 pA/cm/sup 2/ dark current. Performance is limited by pixel 1/f noise, not by the ADC noise floor of 140 /spl mu/V. The column ADC memory employs a custom DRAM to save area. The sensor utilizes a 0.35 /spl mu/m 1P 3M CMOS process.

SXGA pinned photodiode CMOS image sensor in 0.35 /spl mu/m technology

CMOS imagers are commonly employing pinned photodiode pixels and true correlated double sampling to eliminate kTC noise and achieve low noise performance. Low noise performance also depends on optimisation of the readout circuitry. This paper investigates the effect of the pixel source follower transistor on the overall noise performance through several characterization methods. The characterization methods are described, and experimental results are detailed. It is shown that the source follower noise can be the limiting factor of the image sensor and requires optimisation.

Didier Herault

Papers

Color filters including infrared cut-off integrated on CMOS image sensor.

Fully Optimized Cu based process with dedicated cavity etch for 1.75μm and 1.45μm pixel pitch CMOS Image Sensors

SXGA pinned photodiode CMOS image sensor in 0.35 /spl mu/m technology

Source follower noise limitations in CMOS active pixel sensors

12.4 SXGA Pinned Photodiode CMOS Image Sensor in 0.35µm Technology