APPLICATION

Because the CCIS can also be used as a shift register, there is great benefit to use this photodetector in an imaging-array system since the signals can be brought out sequentially to a single node, without complicated x-y addressing to each pixel. This is the main advantage of a focal-plane array which the CCISs are very successful in. The detection mode of integrating charge over long period of time enables detection of weaker signals. This is an important feature for astronomy imaging. Besides these, the CCISs have advantages of low dark current, low-noise and low-voltage operation, good linearity and good dynamic range. The structure is simple and compact, stable and robust, and is compatible with MOS/MIS technology. These factors contribute to high yield which enables the CCISs to be feasible in consumer products. The CCISs can be used in cameras for personal camcorders, broadcasting systems, robot vision, image analysis, astronomy, surveillance, and military aiming, guidance and tracking systems.

The CCIS can also be used as nuclear-radiation detector. One disadvantage of a CCIS is potential damage from light, especially of high-energy radiation. This is a common concern for MOS/MIS devices. Radiation damage is a result of generation of interface traps at the Si-insulator interface and fixed charge in the insulator.

RELATED DEVICE

Charge-Injection Device

The charge-injection device (CID) does not necessarily imply a different structure from a CCIS. The difference lies in the readout mode. Instead of transferring the accumulated charge laterally, the charge-injection device releases the charge to the substrate by lowering the gate voltage. In an area-imaging system, x-y addressing of this photodetector is accomplished by implementing a two-well unit cell. With two closely spaced gates, the photo-generated charge can be shifted between the wells, controlled by the gate voltages. The charge is injected to the substrate only when both gate potentials are lowered and the semiconductor surface is driven into accumulation.

There are two readout mechanisms for the CIDs: sequential injection and parallel injection. In the sequential-injection scheme, a pixel is selected when both gate potentials are left to float, and as the charge is injected into the substrate, a displacement current can be sensed either at the substrate terminal or at the gate. In the parallel injection scheme, a whole row is selected and all columns are read at the same time. A signal is detected when charge is transferred from one well (which has higher gate voltage and/or thinner gate dielectric) to another within the unit cell. In such readout as a displacement current in the gate, the charge is preserved. The CID area arrays have advantage of random access capability. Transfer between cells is not necessary and therefore transfer efficiency is not critical. The trade-off is higher power dissipation which can be improved by an epitaxial substrate, larger noise due to large capacitance of the whole column, and necessity of better sensing amplifier due to weaker signals.