Impactron-a new solid state image intensifier

This paper describes the theory of operation and up to date achieved performance of a new image sensor concept that is using Impact Ionization to multiply photo-generated charge before sensing. It is shown that the charge multiplication based on a single carrier impact ionization is almost noiseless. This allows detected signal charge to be amplified directly in the charge domain and be always kept above the charge detector amplifier noise floor. Charge is repeatedly transferred in a CCD fashion through high field regions where the impact ionization occurs. Even though the impact ionization has a low probability and the high field regions are short the number of transfers is large and significant charge gains are obtained. The developed charge multiplication structure can be easily incorporated into pixels of any standard CCD image sensor and included in the image sensing area, the memory area, or any other vertical or horizontal CCD register with a minimum area penalty. This feature thus provides high flexibility in designing new sensors with various performance characteristics suitable for an extreme low light level imaging. The paper describes in detail the theory of charge multiplication and excess noise generation that is supported by the measured data obtained form the test image sensors. The measurement methods that are used to characterize the charge multiplication gain and noise are also described in detail.