From Photon to Pixel

3The Digital Sensor

The sensor is naturally the key element of the digital photographic camera. Though the first solid detectors were metal-oxide semiconductor (MOS) photodiodes, at the end of the 1960s, it is the charge-coupled devices (CCD) technology, discovered in 1969¹, which has for many years constituted most of the sensors of photo cameras². Since the year 2000, the complementary metal-oxide semiconductor (CMOS) transistor technology developed in 1980s, has concurrently spread for reasons we will see later, it is rapidly becoming the standard. Today, other materials are being developed to improve the performance of the sensor, especially quantum dots in graphene nanostructures [JOH 15, LIU 14] or colloidal crystals [CLI 08], which could eventually deliver exceptional performances regarding both the efficiency of photon/electron conversions (greater than 1) and detection speed. We will quickly address these sensors in the chapter on color, in section 5.4.1.2.

The efforts to develop sensors have taken several directions that all result in a complexification of the manufacturing processes:

• – a densification of the photosites³;
• – an increased performance: sensitivity, linearity, immunity to noises;
• – an integration of processes at the sensor to improve the signal and unburden the central processor of systematic operations.

It is according to these three axes that our presentation will be developed.

3.1. Sensor size

The race for miniaturization has been driven with two ...