CN105552096A - Image sensor chip capable of implementing plasma color filtering on metal layers in pixels - Google Patents

Abstract

The invention discloses an image sensor chip capable of implementing plasma color filtering on metal layers in pixels. The mage sensor chip is characterized by comprising a pixel array, wherein the pixel array comprises multiple pixels; the metal layer in each pixel comprises a plasma color filter; the plasma filters are periodically-arranged through holes, and the arrangement periods can be triangular, square and the like; and the aperture of the through holes is d, and the pitch of the holes is p. According to the image sensor chip, the plasma filters are implemented on the metal layers in the pixels to replace an existing filter lens that is arranged on the top of each pixel and implemented through complex post processing; due to the design of the hole array periods, hole diameters, hole shapes and other determined filtering frequencies for the through holes in the metal layers, the color filters can be directly integrated in the chip; according to the method, the color filters and photodiodes in photosensitive regions are arranged closely, so that a better imaging performance can be achieved; and meanwhile, a method compatible with a standard CMOS process (aluminum layer) is adopted to replace the costly post processing, so that the cost of the image sensor chip is greatly lowered.

Description

An image sensor chip with plasma color filtering implemented on the metal layer inside the pixel

technical field

The invention relates to an integrated circuit sensor and a chip, in particular to an image sensor chip in which a metal layer inside a pixel implements plasma color filtering.

Background technique

The complementary metal oxide semiconductor (CMOS) image sensor market has grown very rapidly in recent years. Compared with traditional digital image charge-coupled device (CCD) technology, its main advantage is that it can integrate electronic modules such as imaging devices, exposure control, analog-to-digital conversion, and signal processing into a single digital camera chip to achieve lower cost and lower power consumption. Power-consuming imaging systems, especially for the fast-growing market of portable devices such as mobile phones and computers. Although image sensor technology has made tremendous progress in recent years, consumers still expect higher resolution, that is, while maintaining the same sensor size, the number of pixels is continuously increased, which will result in a decrease in the light signal received by each pixel, In order to ensure the image quality, higher requirements are put forward for the image sensor technology, that is, to reduce the size, improve the conversion efficiency and reduce the noise, but the existing filter technology limits the further optimization of the pixel process.

The CMOS image sensor realizes color imaging through an organic dye filter, which is located between the optical microlens and the image sensor, and filters the red, green and blue standard three-color spectrum, but this technology has certain limitations. First of all, the filter is an absorbing material, which can only transmit part of the incident light energy, and the light transmission efficiency is very low. Therefore, when the pixel size becomes smaller, the transmitted incident light is very limited, which affects the imaging quality. Second, due to the low absorption coefficient of the filter dye material, there is a certain requirement for the thickness of the filter (greater than several hundred nanometers), which limits the realization of small pixels. In addition, organic dye color filters are not optically stable at high temperature or prolonged UV exposure. In particular, finely aligned lithography is required on the photodiode array and on the filters during the manufacturing process, thereby increasing manufacturing costs.

The latest scientific research results show that structured photonic materials, such as plasmonic filters, can selectively transmit specific narrow-band signals and effectively block other frequency signals, so they are expected to replace organic dye filters to achieve further improvement of image sensor pixel technology. The plasmonic filter is realized by a metal film with a fixed structure of hole arrays. By adjusting the size and spacing of the apertures, the transmission wavelength is in the visible light range (400nm to 800nm). Due to its good narrow-band filtering characteristics, it is very suitable for visible light filter. Here's how it works: You start with a block of metal that contains a negatively charged plasma and a background of positively charged ionic cores, and a displacement of its electron density from the positive core causes an oscillation at a resonant frequency point associated with the material, called the is the plasma frequency. When metal nanoparticles of sub-skin depth thickness are illuminated by a plane-wave light source, the electric field displaces free electrons. The interaction of light with metal nanoparticles will lead to localized surface plasmon resonance (LSPR). When this reaction is close to the plasmonic frequency, this will lead to resonantly enhanced scattering and absorption of incident light, realizing the unique optical properties of metal colloids. Exploring the wavelength-dependent extraordinary optical transmission (EOT, Extraordinary Optical Transmission) interaction with surface plasmon polaritons (SPP, Surface Plasmon Polaritons) through plasmonic filters to realize color filters, providing an ideal alternative to traditional color imaging filters The method has broad application prospects. The main advantages of this technology include: adjustable, that is, the filtering of different wavelengths of visible light can be achieved by scaling the array period and the diameter of the holes; easy to manufacture, usually aluminum is an ideal material in practical applications, due to its low dielectric loss, only There is a need for a material that can filter light of different colors; it is low-cost, can be produced by a standard CMOS process, and is compatible with the production process of the image sensor.

The existing plasma-implemented filter method (StanleyP.Burgos, ColorImagingviaNearestNeighborHoleCouplinginPlasmonicColorFiltersIntegratedontoaComplementaryMetal-OxideSemiconductorImageSensor, NanoLetter, vol.7, no.11, pp.10038–10047, 2013.) attaches a thin metal film with an array of apertures to the image The top of the sensor implements a color filter, as shown in Figure 1. The filtering frequency of the filter is adjusted by changing the characteristics of the hole array (such as size, spacing, periodicity, shape, etc.), so the plasmonic filter can use a single layer of metal to achieve the filtering of many colors of light. In other words, traditional organic dyed filters need to design a specific dye process for each color, while plasma filters can filter any color through only one layer of metal film. In Figure 1, each hole is circular, and the optimal size diameter and arrangement period of the plasma hole array can be designed for the color to be filtered. Although plasmonic filters have advantages over conventional organic dyes for imaging applications, integrating plasmonic filters on top of image sensors requires complex post-processing steps that significantly increase the cost. In addition, how to precisely align the image sensor and the plasmonic filter is also an urgent problem to be solved.

Contents of the invention

Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides an image sensor chip in which the metal layer inside the pixel implements plasma color filtering. By directly implementing plasma color filtering on the metal layer inside the pixel, the existing Insufficient image sensor.

Technical solution: In order to achieve the above object, the technical solution adopted by the present invention is: an image sensor chip in which the metal layer inside the pixel implements plasma color filtering, which is characterized in that it includes a pixel array, and the pixel array includes several pixels. A plasma color filter is included on the metal layer, and the plasma color filter is a through hole with a periodic arrangement; the size of the aperture of the through hole is d, and the hole spacing is p;

It includes a fast column-parallel signal reading circuit connected to the pixel array, and the signal reading circuit includes a row decoder, a row driver, a column decoder, a column driver, a column-parallel gain-adjustable amplifier, a column-parallel analog-to-digital converter, a static Random access memory, sensitive amplifier, low-voltage differential signal readout module, static register, timing control module and digital control current source;

Under the action of the row decoder and the row driver, the signal of the pixel array is read row by row to the column parallel gain adjustable amplifier and the column parallel analog-to-digital converter; the signal of the column parallel analog-to-digital converter passes through the column decoder and The control of the column driver is read out to the SRAM and the sense amplifier in groups, and finally the data is output to the chip through the high-speed low-voltage differential signal readout module; among them, the timing control module controls the row decoder, the row driver, the column decoder and the column driver. Work; the static register controls the gain variation of the column-parallel gain-adjustable amplifier; the digital control current source provides the bias current to the column-parallel gain-adjustable amplifier and the column-parallel analog-to-digital converter.

Further, the arrangement of the through holes includes a triangular periodic arrangement or a square periodic arrangement.

Further, the through holes include circular holes, octagonal holes and square holes.

Further, the through-hole aperture d and hole spacing p are set as follows according to light of different wavelengths:

Green light: d = 180 nm; p = 340 nm;

Red light: d=240 nm; p=420 nm;

Blue light: d = 140 nm; p = 260 nm.

Beneficial effects: the present invention provides an image sensor chip in which the internal metal layer of the pixel is implemented with plasma color filtering, and the internal metal layer manufactured by the standard CMOS image sensor semiconductor process is used to directly realize the plasma filter on the pixel, so as to meet the continuous shrinkage of the pixel trend. The filter frequency can be determined by the metal hole array period (hole spacing distance, p), hole diameter (d) and hole shape, so that the red, green and blue filters can be directly integrated inside the CMOS image sensor chip. At the same time, the image sensor chip uses a high-speed column-parallel signal readout circuit. Specifically, it has the following advantages:

(1) The present invention directly implements a plasma filter on the metal layer inside the pixel, and the distance between the filter and the photodiode in the photosensitive area implemented on the substrate is close, so that better imaging performance can be obtained;

(2) The present invention adopts a method compatible with the standard CMOS process (aluminum layer) to replace expensive post-processing, which greatly saves costs;

(3) The present invention also provides a fast column-parallel signal reading circuit suitable for large array sensors, which integrates the sensor array and the reading circuit on the same chip, directly converts the sensing signal into a digital signal output, and improves the frame rate .

Description of drawings

FIG. 1 is a structural diagram of a conventional plasma filter manufactured above an image sensor pixel through a post-processing process;

Fig. 2 is a circular hole in a triangular periodic arrangement on the metal layer as a plasma color filter;

Figure 3 is a top view of the design of plasma color filters with different hole shapes;

Figure 4(a) is a cross-sectional view of a pixel of a traditional organic dye filter image sensor;

Figure 4(b) is a cross-sectional view of a pixel of a plasma filter image sensor implemented outside the pixel;

Figure 4(c) is a cross-sectional view of a plasmonic filter image sensor pixel implemented in a pixel;

5 is a top view of the pixel array of the present invention;

FIG. 6 is a structure diagram of the chip of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

An image sensor chip in which the metal layer inside the pixel implements plasma color filtering, as shown in Figure 5, includes a pixel array, the pixel array includes several pixels, and the metal layer inside each pixel includes a plasma color filter, and the plasma filter The color elements are through holes arranged periodically; the through holes are arranged periodically in a square, as shown in FIG. 2 , and may also be arranged periodically in a triangle. And not limited to square and triangular periodic arrangements.

As shown in FIG. 3 , the through holes include circular holes, octagonal holes and square holes; and are not limited to these shapes, and through holes of appropriate shapes can be selected as required. The size of the aperture of the through hole is d, and the hole spacing is p; when the through hole is circular, the aperture size d is the diameter of the circle; when the through hole is a square, the aperture size d is the side length of the square; when the through hole is eight In the case of an octagon, the aperture size d is the distance between two parallel sides of the octagon.

For different wavelengths of light, different aperture designs are required: the most optimal settings for different wavelengths of light are as follows:

The wavelength of green light is 550 nanometers: d=180 nanometers; p=340 nanometers;

The wavelength of red light is 650 nanometers: d=240 nanometers; p=420 nanometers;

Blue light wavelength is 450 nm: d = 140 nm; p = 260 nm.

Figure 4(a) shows the traditional image sensor to achieve color imaging by using absorbing organic dye filters. These filters are located on the upper part of the image sensor pixel, between the microlens and the photodetector PD, and transmit typical red, green and blue Three-color spectrum, but the traditional organic dye filter limits the further reduction of pixel size. Since they transmit only a portion of the visible spectrum, these filters are inherently inefficient in conversion.

Figure 4(b) is a plasmonic filter image sensor pixel implemented outside the pixel, however, integrating the plasmonic filter on top of the image sensor requires complex post-processing steps, which significantly increases the cost; in addition, how to precisely align the image sensor And plasma color filters are also a burning issue.

Figure 4(c) is a plasmonic image sensor pixel implemented in the pixel proposed by the present invention, and the plasmonic filter is directly implemented on the metal layer inside the pixel. Since this method is compatible with the standard CMOS manufacturing process, post-processing is not required , so the production cost can be significantly reduced.

FIG. 5 is a schematic top view of the pixel array of the present invention. Different hole shapes are selected corresponding to different light filtering requirements to form a Bayer distribution. Taking the 2x2 pixel area as an example, corresponding to each 2x2 pixel arrangement area in the pixel array, two pixels at the opposite corner are selected to realize the color filtering of green light with a circular through hole design, and the other two pixels are designed with square and eight The polygons realize the color filtering of red light and blue light respectively. Note that the three through holes are arranged in a consistent square cycle at this time, and corresponding changes can also be made. The through holes in each 2x2 pixel area are arranged periodically with the same shape, and the shape of the through holes and the shape of the periodic arrangement can be selected according to actual needs.

Fig. 6 is an architecture diagram of an image sensor chip of the present invention, which specifically includes a fast column-parallel signal reading circuit connected to a pixel array, and the signal reading circuit includes a row decoder, a row driver, a column decoder, a column driver, and a column-parallel signal reading circuit. Gain adjustable amplifier, column-parallel analog-to-digital converter, SRAM, sensitive amplifier, low-voltage differential signal readout module, static register, timing control module and digital control current source;

Under the action of the row decoder and the row driver, the signal of the pixel array is read row by row to the column parallel gain adjustable amplifier and the column parallel analog-to-digital converter; the signal of the column parallel analog-to-digital converter passes through the column decoder and The control of the column driver is read out to the SRAM and the sense amplifier in groups, and finally the data is output to the chip through the high-speed low-voltage differential signal readout module; among them, the timing control module controls the row decoder, the row driver, the column decoder and the column driver. Work; the static register controls the gain variation of the column-parallel gain-adjustable amplifier; the digital control current source provides the bias current to the column-parallel gain-adjustable amplifier and the column-parallel analog-to-digital converter.

The above descriptions are only preferred embodiments of the present invention, and the present invention is also applicable to filters of other spectral frequency bands besides visible light, such as infrared light and the like. It should be pointed out that for those skilled in the art, some improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (4)

1. the image sensor chip of pixel inner metal layer enforcement plasma colour filter, it is characterized in that, comprise pel array, pel array comprises some pixels, the metal level of each pixel inside comprises plasma colour filter, and described plasma colour filter is the through hole with periodic arrangement; The size in the aperture of described through hole is d, and pitch of holes is p;

Comprise the quick row parallel signal reading circuit be connected with pel array, described signal read circuits comprises row decoder, line driver, column decoder, row driver, row parallel gain adjustable amplifier, row parallel A/D converter, static random access memory, sense amplifier, Low Voltage Differential Signal reading module, static register, time-sequence control module and digital control current source;

Pel array is under the effect of row decoder and line driver, and the signal of pel array is read out line by line row parallel gain adjustable amplifier and row parallel A/D converter; The signal of row parallel A/D converter is through the control of column decoder and row driver, and grouping reads into static random access memory and sense amplifier, reads module by data pio chip eventually through high velocity, low pressure differential signal; Wherein, the work of time-sequence control module control lines decoder, line driver, column decoder and row driver; Static register controls the change in gain of row parallel gain adjustable amplifier; Digital control current source provides bias current to row parallel gain adjustable amplifier and row parallel A/D converter.

2. a kind of pixel inner metal layer implements the image sensor chip of plasma colour filter as claimed in claim 1, it is characterized in that, described arrays of openings mode comprises triangular shaped periods arrangement or foursquare periodic arrangement.

3. a kind of pixel inner metal layer implements the image sensor chip of plasma colour filter as claimed in claim 2, and it is characterized in that, described through hole comprises circular port, octagon hole and square hole.

4. a kind of pixel inner metal layer implements the image sensor chip of plasma colour filter as claimed in claim 3, and it is characterized in that, described through-hole aperture d and pitch of holes p is as follows according to the light settings of different wave length:

Green glow: d=180 nanometer; P=340 nanometer;

Ruddiness: d=240 nanometer; P=420 nanometer;

Blue light: d=140 nanometer; P=260 nanometer.