An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

Digital radiography offers the potential of improved image quality as well as providing opportunities for advances in medical image management, computer-aided diagnosis and teleradiology. Image quality is intimately linked to the precise and accurate acquisition of information from the x-ray beam transmitted by the patient, i.e. to the performance of the x-ray detector. Detectors for digital radiography must meet the needs of the specific radiological procedure where they will be used. Key parameters are spatial resolution, uniformity of response, contrast sensitivity, dynamic range, acquisition speed and frame rate. The underlying physical considerations defining the performance of x-ray detectors for radiography will be reviewed. Some of the more promising existing and experimental detector technologies which may be suitable for digital radiography will be considered. Devices that can be employed in full-area detectors and also those more appropriate for scanning x-ray systems will be discussed. These include various approaches based on phosphor x-ray converters, where light quanta are produced as an intermediate stage, as well as direct x-ray-to-charge conversion materials such as zinc cadmium telluride, amorphous selenium and crystalline silicon.

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X-ray detectors for digital radiography

The basic physics underlying the operation and key performance issues of amorphous-silicon thin-film transistors (TFTs) are discussed. The static transistor characteristics are determined by the localized electronic states that occur in the bandgap of the amorphous silicon. The deep states, mostly consisting of Si dangling bonds, determine the threshold voltage, and the conduction band-tail states determine the field-effect mobility. The finite capture and emission times of the deep localized states lead to a dynamic transistor characteristic that can be described by a time-dependent threshold voltage. The transistors also show longer time threshold voltage shifts due to two other distinct mechanisms: charge trapping in the silicon nitride gate insulator and metastable dangling bond state creation in the amorphous silicon. These two mechanisms show characteristically different bias, temperature, and time dependencies of the threshold voltage shift. Illumination of a TFT causes the generation of electron-hole pairs in the space-charge region leading to a steady-state equal flux of electrons and holes and a reduction in the band-bending. In most applications, the photosensitivity should be minimized. The uniformity of large arrays of transistors for display applications is excellent, with variations in the threshold voltage of 0.5-1.0 V. >

The physics of amorphous-silicon thin-film transistors

PURPOSE: To describe the design and performance of a novel frameless system for radiosurgery. This technology, called image-guided radiosurgery (IGR), eliminates the need for stereotactic frame fixation by relating the identified lesion to radiographic landmarks. CONCEPT: IGR uses a lightweight x-band linear accelerator, computer-controlled robotic arm (Fanuc manipulator [Fanuc Robotics North America, Inc., Rochester Hills, MI]), paired orthogonal x-ray imagers, and a computer workstation that performs rapid image-to-image registration. During radiosurgery, the x-ray imaging system determines the location of the lesion and communicates these coordinates to the robot, which adjusts the pointing of the linear accelerator beam to maintain alignment with the target. RATIONALE: Existing stereotactic techniques require rigid cranial fixation to establish and maintain a system of reference for targeting. Such frames cause pain for the patient, limit the use of fractionation, and necessitate a prolonged period of general anesthesia if children are to be treated. Furthermore, skeletal or any other type of rigid fixation is difficult to achieve beyond the cranium. IGR was designed to overcome these limitations, which are inherent to nearly all current radiosurgical methods. DISCUSSION: Preliminary testing and early clinical experience have demonstrated the practicality and potential of the IGR concept and have identified the most important directions for improvement. For example, an IGR prototype accurately tracked target displacements in three dimensions but showed reduced accuracy when confronted by rotational movements. This observation led to development of a new generation of tracking algorithm that promises to improve tracking in all six dimensions. Further experience indicated that improvements in the quality of the x-ray images were needed to allow the system to locate and treat target sites outside the cranium. Consequently, a new x-ray imaging technology with superior resolution and increased sensitivity has been added to the system. These improvements should make it possible to apply IGR techniques to a variety of targets located throughout the body. This article describes and critiques the components of the IGR and summarizes our preliminary clinical experience.

Image-guided robotic radiosurgery

A photodiode has integrated shields for the rejection of noise-producing electromagnetic interference and ambient light. The electromagnetic shield forms a conductive matrix which covers the photodiode active area. The matrix is deposited as a metallization layer onto the photodiode and provides exposed portions of the active area for light detection. A pad is electrically connected to the shield to allow external termination of the shield. The ambient-light shield is in the form of a colored encapsulant surrounding the photodiode. The encapsulant provides a high-pass light transmission characteristic which passes signal light and rejects out-of-band ambient light. The photodiode is particularly advantageous for use in pulse oximetry probes.

Photodiode detector with integrated noise shielding

A photodetecting device and a method for constructing the photodetecting device. The photodetecting device provides at least one transistor formed over a substrate and at least one photodiode formed over the at least one transistor. Each of the at least one photodiode is coupled to one of the at least one transistor. The fill factor of the photodiode is very high even when the resolution of the photodetecting device is increased. The photodetecting devices are formed in a matrix having rows and columns. The matrix of photodetecting devices forms a two dimensional imaging device.

Layered solid state photodiode sensor array

Recombination in a -Si: H: Transitions through defect states

Large two dimensional amorphous silicon image sensor arrays offer a new approach to electronic document input and x-ray imaging. The sensor array technology is now capable of image capture at greater than 10 frames/sec and with resolution of 200–400 spi. We describe our new high resolution imaging system, comprising a page-sized sensor array with nearly 3 million pixels, and the accompanying high speed read out and processing electronics. The key technological issues of pixel resolution, sensor fill factor, leakage currents and noise are reviewed. Measurements of a new array architecture are described, in which the sensor is formed as a single continuous film on top of the matrix addressing components.

Two Dimensional Amorphous Silicon Image Sensor Arrays

This paper introduces new high-resolution amorphous Silicon (a-Si) image sensors specifically configured for demonstrating film-quality medical x-ray imaging capabilities. The devices utilizes an x-ray phosphor screen coupled to an array of a-Si photodiodes for detecting visible light, and a-Si thin-film transistors (TFTs) for connecting the photodiodes to external readout electronics. We have developed imagers based on a pixel size of 127 micrometer X 127 micrometer with an approximately page-size imaging area of 244 mm X 195 mm, and array size of 1,536 data lines by 1,920 gate lines, for a total of 2.95 million pixels. More recently, we have developed a much larger imager based on the same pixel pattern, which covers an area of approximately 406 mm X 293 mm, with 2,304 data lines by 3,200 gate lines, for a total of nearly 7.4 million pixels. This is very likely to be the largest image sensor array and highest pixel count detector fabricated on a single substrate. Both imagers connect to a standard PC and are capable of taking an image in a few seconds. Through design rule optimization we have achieved a light sensitive area of 57% and optimized quantum efficiency for x-ray phosphor output in the green part of the spectrum, yielding an average quantum efficiency between 500 and 600 nm of approximately 70%. At the same time, we have managed to reduce extraneous leakage currents on these devices to a few fA per pixel, which allows for very high dynamic range to be achieved. We have characterized leakage currents as a function of photodiode bias, time and temperature to demonstrate high stability over these large sized arrays. At the electronics level, we have adopted a new generation of low noise, charge- sensitive amplifiers coupled to 12-bit A/D converters. Considerable attention was given to reducing electronic noise in order to demonstrate a large dynamic range (over 4,000:1) for medical imaging applications. Through a combination of low data lines capacitance, readout amplifier design, optimized timing, and noise cancellation techniques, we achieve 1,000e to 2,000e of noise for the page size and large size arrays, respectively. This allows for true 12-bit performance and quantum limited images over a wide range of x-ray exposures. Various approaches to reducing line correlated noise have been implemented and will be discussed. Images documenting the improved performance will be presented. Avenues for improvement are under development, including higher resolution 97 micrometer pixel imagers, further improvements in detective quantum efficiency, and characterization of dynamic behavior.

New amorphous-silicon image sensor for x-ray diagnostic medical imaging applications

Large two-dimensional amorphous silicon image sensor arrays offer an advantage for high speed document scanning and medical X-ray imaging. We describe our page sized 200 spot per inch imager and the accompanying high speed readout electronics. The spatial resolution performance for white light and X-ray imaging is illustrated. We discuss how the important issues of noise and resolution depend on the properties of a-Si:H, and show how the material can be used to give improved performance of the imagers.

Richard L. Weisfield

Papers

Layered solid state photodiode sensor array

Recombination in a -Si: H: Transitions through defect states

Two Dimensional Amorphous Silicon Image Sensor Arrays

New amorphous-silicon image sensor for x-ray diagnostic medical imaging applications

Two-dimensional amorphous silicon image sensor arrays