Tech Briefs

Ultra-Miniature Image Sensor

A wafer-level camera operates at low power and may be customized for application needs, which include endoscopy, surgical robots, and 3D model generation.

Minimally invasive surgery has increasingly required imaging devices to have the smallest possible dimensions but also deliver high-resolution vision capabilities. There has also been a rising demand for disposable medical devices. With these criteria in mind, in 2004, the first prototype of the NanEye sensor was created in the lab. The miniature 0.25 mm2 camera module measured 0.5 mm × 0.5 mm, with 140 × 140 pixels at a frame rate of 40 frames/second.

NanEye family of image sensors is suitable for integration into endoscopy and surgical robot applications." class="caption" align="right">Further research and development yielded the NanEye 2B image sensor. It is considered a wafer-level camera, meaning that no external components, not even an external capacitor, are needed to run the sensor. This digital camera’s head dimensions are 1 mm × 1 mm × 1.5 mm. The optionally available optics include one aspherical surface and one aperture. It is glued directly on the image sensor and has its best focus position designed in, so no mechanical focus correction is required.

The NanEye is customizable to OEMs’ application needs, which include integration into endoscopy, dental imaging, and surgical robot solutions that call for miniaturization as well as exacting precision. Furthermore, 3D model generation, guidewire visualization, intubation equipment visualization, disposable equipment, and imaging for medical analysis equipment are other possible medical applications.

The lens of the sensor is based on B33 (Borofloat glass) and designed such that the surface toward the object is flat. This is so that the lens performance is not influenced by the medium between the object and lens. Therefore, only the opening angle of the lens is reduced when the system operates in liquid, which is important in applications that involve contact with body fluids. Meanwhile, the lens does not increase the diameter of the sensor, making the NanEye the world’s smallest compact digital camera.

With a total of 250 × 250 pixels at 3 μm pitch rolling shutter, the sensors provide clear and sharp color images utilizing color filters implementing the standard Bayer pattern. The sensor is wire bonded on a flex substrate. The standard length is 56 cm, but may be increased if necessary. The maximum length the camera can drive the signal, without external components, is 2.5 meters. The flex cable has a width of 700 μm and a diameter of 1.5 mm at the tip where the sensor is mounted. The thickness of Flex cable is 65 μm. A very small bend radius can be achieved, down to ~100 μm. Power consumption is consequently minimized and is only 5 mW operating at 44 frames/second. A low power variation using only 600 μA from 1.8 V supply is also available for battery-powered applications.

Image data are transmitted over a 10-bit digital LVDS using an in-house developed data transmission protocol. Optionally available software enables the camera to run on a PC in real time with image corrections. The software runs under Microsoft Windows XP and includes a USB driver. It displays the image on a PC in real time and performs a number of functions such as offset and gain correction for delay-free, smooth video operation.

This technology was done by AWAIBA, Madeira, Portugal. For more information, visit http://info.hotims.com/34453-196.