Abstract
This paper explains the device structure and operation of image sensors and solar cells. Both are semiconductor devices operating with the same physical principle of detecting photons. A high efficiency of the photon to electron energy conversion is very much desired in both devices. Image sensors now use a very advanced and scaled down CMOS fabrication process technology to achieve high performance features such as the excellent short wave blue light sensitivity for good color reproduction, the low noise and the no image lag picture quality for filmless and mechanical free action cameras. On the other hand, solar cells are still now built with the primitive floating N+P single junction type photodiode to minimize the fabrication process cost but with very low energy conversion efficiency of about 20%. It is explained in details that the depletion region of the PN junction is not the only place where we can achieve photo electron and hole pair separations effectively. The short-wave blue light has only 1000 Å silicon crystal penetration depth. The pinned surface P+P Gaussian doping profile has a very important role to achieve a better photon to energy conversion efficiency, especially for the short-wave blue light. Electrostatic and dynamic behaviors of Pinned Surface P+PNP Double Junction type Dynamic Photo Transistor and Pinned Surface P+PNPN Triple Junction type Dynamic Photo Thyristor are analyzed in details. Both of them are shown to be expected to have much excellent photon-to-electron energy conversion efficiency.
Highlights
The human eye balls convert the light energy to the electron energy
The long line of nerve cells acts as a Charge Transfer Device (CTD) while the human brain acts as a central processing unit (CPU) and an information memory storage
Instead of the CCD/metal oxide semiconductor (MOS) dynamic photo capacitor type Global Shutter buffer memory, Figure 24 shows a floating diffusion (FD) type Global Shutter buffer memory which is equipped with an in-pixel active photo sensor with the source follower current amplifier read-out circuit and with the double junction P+PNPP+ type Pinned Photodiode P+ pinned surface and the buried N type photo electron charge storage region
Summary
The human eye balls convert the light energy to the electron energy. The in-coming light thru the iris excites the retinal cells inside a human eye ball. A typical image sensor is composed of three parts likewise They are (1) the photo detecting device (PPD) like the retina cells, (2) the Charge Transfer Device (CTD) like the long line of nerve cells and (3) the signal processing CPU and Memory Units like the human brain. In a typical classical MOS type CTD image sensor the first part is a single N+P floating diffusion junction type dynamic photo capacitor type PPD. Sony focused in producing the image sensor products It took more than ten years for Sony to develop the ILT CCD type image sensor with the PNPN triple junction type dynamic photo thyristor with the completely mechanical-part free electrical shutter function and completely image lag free feature [8]. Sony introduced in 1987 the passport size compact video camera using this Pinned Photodiode which was originally invented by Yoshiaki Hagiwara at Sony in 1975
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