Patent Application
20140078356
This relates generally to imaging devices, and more particularly, to imaging devices with high dielectric constant barrier layers.
Modern electronic devices such as cellular telephones, cameras, and computers often use digital image sensors. Imagers (i.e., image sensors) may be formed from image sensing pixels. Each pixel may include a photosensor such as a photodiode that receives incident photons (light) and converts the photons into electrical signals. Image sensors are sometimes designed to provide images to electronic devices using a Joint Photographic Experts Group (JPEG) format or any other suitable image format.
In conventional backside illumination (BSI) image sensors, a color filter array is formed over the photodiodes to provide each pixel with sensitivity to a certain range of wavelengths. An array of microlenses is typically formed over the color filter array. Light enters the microlenses and travels through the color filters to the photodiodes. Each photodiode converts incident photons (light) into electrical signals which are then passed through additional imaging system circuitry.
While BSI image sensors enable smaller pixel sizes without the optical losses that are often associated with standard front-side illuminated sensors, one concern of BSI image sensors is the close proximity of color filter materials to the active silicon of the photodiodes. If care is not taken, the ionic contaminants that are intrinsic to color filter pigments and the high refractive index of the silicon may result in reflective losses at the silicon surface.
It would therefore be desirable to be able to provide imaging systems with improved optical efficiency.
Electronic devices such as digital cameras, computers, cellular telephones, and other electronic devices include image sensors that gather incoming light to capture an image. The image sensors may include arrays of imaging pixels. The pixels in the image sensors may include photosensitive elements such as photodiodes that convert the incoming light into image signals. Image sensors may have any number of pixels (e.g., hundreds or thousands of pixels or more). A typical image sensor may, for example, have hundreds of thousands or millions of pixels (e.g., megapixels). Image sensors may include control circuitry such as circuitry for operating the imaging pixels and readout circuitry for reading out image signals corresponding to the electric charge generated by the photosensitive elements.
Image sensor 16 may include an array of image sensor pixels and a corresponding array of color filter elements.
Processing circuitry 18 may include one or more integrated circuits (e.g., image processing circuits, microprocessors, storage devices such as random-access memory and non-volatile memory, etc.) and may be implemented using components that are separate from camera module 12 and/or that form part of camera module 12 (e.g., circuits that form part of an integrated circuit that includes image sensors 16 or an integrated circuit within module 12 that is associated with image sensors 16). Image data that has been captured by camera module 12 may be processed and stored using processing circuitry 18. Processed image data may, if desired, be provided to external equipment (e.g., a computer or other device) using wired and/or wireless communications paths coupled to processing circuitry 18.
Color filters 112 (also referred to as color filter elements) may be separated from photodiodes 106 within substrate 108 by barrier layer 110 such that photodiodes 106 are protected from ionic contaminants that are intrinsic to color filter pigments in color filters 112. Barrier layer 110 may be interposed between color filters 112 and substrate layer 108 and may have a thickness of 100-500 Angstroms, 200-400 Angstroms, 100-1000 Angstroms, or any other suitable thickness. Barrier layer 110 may be formed from a transparent material having a high dielectric constant that is above a given threshold. Materials with high dielectric constants are sometimes referred to as “high-k” materials, or materials that have a higher dielectric constant “k” than the dielectric constant for silicon dioxide. For example, high-k materials used to form barrier layer 110 may include materials with dielectric constants above 3.9, between 3.9 and 3000, between 20 and 200, or any other suitable “high-k” dielectric constant. Forming a layer of high-k material on substrate layer 108 may help minimize reflective losses at the surface of substrate layer 108 while also helping to reduce dark current in the image sensor. Barrier layer 110 (sometimes referred to as dielectric layer 110) may be formed from one or more high-k oxides or may be formed from a multi-oxide solid solution. Forming dielectric layer 110 from a multi-oxide solid solution may inhibit crystallization of dielectric layer 110. Barrier layer 110 may be configured to function as a thin surface capacitor and may help repel negative charge at the active silicon surface of photodiodes 106 in substrate layer 108.
High-k oxides that may be used to form barrier layer 110 may include zirconium dioxide (ZrO2), titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), strontium titanate (SrTiO3), barium titanate (BaTiO3), yttrium oxide (Y2O3), tellurium dioxide (TeO2), and zinc oxide (ZnO). Additional materials that may be used to form barrier layer 110 may include lanthanide oxides such as ytterbium oxide (Yb2O3), lutetium oxide (Lu2O3), and dysprosium oxide (Dy2O3). Barrier layer 110 may be formed from solid solutions of any suitable mixtures of the above-mentioned high-k oxides, either with each other, or with materials having lower dielectric constants such as aluminum oxide (Al2O3) or silicon dioxide (SiO2).
Barrier layer 110 may also be formed from one or multiple nanolaminate structures, which are multilayered thin film structures with nanometer dimensions. The nanolaminate structure may be formed from nanolayers of any suitable combination of the above-mentioned high-k oxides with each other or with materials having lower dielectric constants such as such as aluminum oxide (Al2O3) or silicon dioxide (SiO2). The thickness of each nanolayer may be 0.2-200 nanometers or 0.2-1000 nanometers. The nanolayers may be deposited using any suitable deposition methods and equipment for depositing nanolayers, such as atomic layer deposition using atomic layer deposition equipment, sputtering using sputtering equipment, or chemical vapor deposition using chemical vapor deposition equipment. The nanolayers may then be laminated together using any suitable lamination method and lamination equipment. For example, a first nanolayer of a high-k oxide may be laminated to a second nanolayer of a different high-k oxide to form a nanolaminate that may be used to form barrier layer 110.
The high-k materials of barrier layer 110 may help minimize reflective losses at the silicon surface substrate 108, thereby eliminating the need for an additional antireflective coating on the surface of substrate 108. This is, however, merely illustrative. If desired, barrier layer 110 may be used in conjunction with an additional antireflective coating such as antireflective coating layer 111. Barrier layer 110 may also be used in conjunction with an optional thin passivation layer such as layer 113-A. Layer 113-A may be a passivation layer formed from SiO2. Passivation layer 113-A may be interposed between barrier layer 110 and photodiodes 106 and/or may be interposed between barrier layer 110 and color filters 112. If desired, a first passivation layer such as layer 113-A may be interposed between the barrier layer 110 and substrate 108 and a second passivation layer such as layer 113-B may be interposed between the color filters 112 and barrier layer 110.
Any suitable combination and arrangements of barrier layer 110, optional layer 111, optional layer 113-A, and optional layer 113-B may be used: antireflective layer 111 may be interposed between photodiode array 106 and passivation layer 113-A with or without passivation layer 113-B; passivation layer 113-A may be interposed between antireflective layer 111 and photodiode array 106 with or without passivation layer 113-B; barrier layer 110 may be interposed between antireflective layer 111 and passivation layer 113-B with or without passivation layer 113-A; and barrier layer 110 may be interposed between passivation layers 113-A and 113-B with or without antireflective layer 111. There may also be any suitable number of high-k oxide barrier layers 110 interposed between the array of photodiodes 106 and the array of color filters 112.
Processor system 300, which may be a digital still or video camera system, may include a lens such as lens 396 for focusing an image onto a pixel array such as pixel array 201 when shutter release button 397 is pressed. Processor system 300 may include a central processing unit such as central processing unit (CPU) 395. CPU 395 may be a microprocessor that controls camera functions and one or more image flow functions and communicates with one or more input/output (I/O) devices 391 over a bus such as bus 393. Imaging device 200 may also communicate with CPU 395 over bus 393. System 300 may include random access memory (RAM) 392 and removable memory 394. Removable memory 394 may include flash memory that communicates with CPU 395 over bus 393. Imaging device 200 may be combined with CPU 395, with or without memory storage, on a single integrated circuit or on a different chip. Although bus 393 is illustrated as a single bus, it may be one or more buses or bridges or other communication paths used to interconnect the system components.
Various embodiments have been described illustrating image sensors that have barrier layers formed from high dielectric constant materials. A system may include an image sensor module with an array of image sensor pixels and one or more lenses that focus light onto the array of image sensor pixels (e.g., image pixels arranged in rows and columns). The array of image sensor pixels may include a color filter array interposed between an array of photosensors and an array of microlenses. Image sensors with barrier layers of the type shown in
In particular, an image sensor may include a transparent barrier layer interposed between an array of photodiodes and an array of color filter elements. The barrier layer may be formed from a material having a high dielectric constant such as a high-k material. The barrier layer may act as an antireflective coating over the photodiodes. A high-k oxide material, including lanthanide oxides, may be used to form the barrier layer. The barrier layer may, for example, be formed from one or more high-k oxides or may be formed from one more high-k oxides mixed with aluminum oxide or silicon dioxide in a solid multi-oxide solution. The barrier layer may be a nanolaminate structure formed from layers of two or more dielectric materials, at least one of which is a high-k oxide material. The high-k barrier layer may have a thickness of 100-500 Angstroms and may be deposited on an image sensor substrate using any suitable deposition process and equipment known in the art (e.g. physical vapor deposition, chemical vapor deposition, sputtering, etc.).
A passivation layer such as a silicon dioxide passivation layer may be formed between the high-k barrier layer and the array of photodiodes or may be formed between the high-k barrier layer and the color filter layer. If desired, there may be silicon dioxide passivation layers above and below the high-k barrier layer.
The foregoing is merely illustrative of the principles of this invention which can be practiced in other embodiments.
This application claims the benefit of provisional patent application No. 61/703,653, filed Sep. 20, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61703653 | Sep 2012 | US |
