Wafer-scale CMOS imaging enters X-ray applications

June 20, 2012 // By Julien Happich
Wafer-scale CMOS imaging enters X-ray applications
The Science and Technology Facilities Council's (STFC) Rutherford Appleton Laboratory (RAL) has developed a high-resolution wafer-scale digital image sensor that targets medical imaging applications.

The STFC's CMOS Sensor Design Group designed a 120x145 mm sensor to be 'butted' or 'tiled' together in a 2 x 2 arrangement, effectively using an entire 200 mm silicon wafer in its production.
The primary target application for the new sensor is X-ray medical imaging and more specifically mammography and digital tomosynthesis, the advanced diagnostic technique used to generate 3D representations of patients or other scanned objects. There is increasing interest in the use of solid-state-based X-ray detection systems in the replacement of conventional diagnostic imaging techniques. One of these technologies is CMOS sensor based imaging, which can bring key advantages in terms of performance such as high resolution, high dynamic range and low noise capabilities.

As no lens is used in CMOS-imaging-based X-ray applications, the size of an image sensor has to match the size of the target area. While in some medical imaging applications such as extra-oral panoramic dental imaging, a sensor measuring 139 x 120 mm is usually adequate, mammography applications require a sensor that is approximately 290x240 mm in size, and even larger for chest radiography. In other applications such as full body scanning for security purposes, an even more extensive sensor area can be necessary.

A three-sided 'buttable' sensor design
The new STFC high-resolution and radiation-hard CMOS sensor has been developed to meet these challenges. A unique feature of the device is that it has sensing pixels right up to the edges on three sides of the imager. This allows multiple sensors, manufactured on cost-effective 200 mm silicon wafers, to be 'butted' or 'tiled' together in a 2x2 arrangement to form a significantly larger imaging area and to meet the requirements for mammography applications. Additionally, any 2xN sensor arrangements are possible, thus making the device suitable for applications that demand even larger area coverage, such as chest imaging or security scans.


Traditionally CMOS imagers have the required electronic circuitry implemented on two sides

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