CMOS Image Sensors

An image sensor is a device that converts a visual image to an electric signal, which is used mostly in digital cameras and other imaging devices. It is a set of charge-coupled device (CCD) or active-pixel sensors (APS) like CMOS sensors. The pixel responds to the light by accumulating charges - the more light, the more charge. Thereby the optical signal is transformed into an electric signal, which gets converted into digial information. Compared to CCD, CMOS sensors are faster, smaller, and cheaper as they are more integrated, which makes them also more power efficient.

CMOS image sensor (CIS) modules combine a CIS die with an optical system, a processor, and passives into a single package, such as chip-on-board, chip-scale packaging, or flipchip. A typical camera module is composed of an image sensor die, a carrier (ceramic or laminate), an IR filter, a lens barrel with optical elements, a lens holder, a processing chip, passive components and a flexible lead with connectors. Currently, the general concept of camera module assembly undergoes a transition from discrete assembly to wafer-level integration using well-established semiconductor technologies.

Wafer-level cameras (WLCs) are devices in which all individual parts are fabricated at wafer level, which are then bonded to form one single part composed of a CIS and a micro-optics stack, enhancing the light-capture efficiency of the camera. WLCs have already started to replace conventional modules due to their smaller form factor and lower cost. The latest version of WLCs has wafer-level optics, wafer-level packaging, and back-side illumination.


Conventional camera vs. wafer level camera. Courtesy of Tessera.