Photoelectric converting film stack type solid-state image pickup device

Abstract

A photoelectric converting film stack type solid-state image pickup device comprising: a semiconductor substrate in which a signal read circuit is formed; and at least one photoelectric converting film interposed between two electrode films, said at least one photoelectric converting film being stacked above the semiconductor substrate, wherein a signal corresponding to an intensity of incident light is read outside by the signal read circuit, the signal being generated by photoelectric conversion with the photoelectric converting film, wherein the photoelectric converting film comprises: a first layer comprising: an ultrafine particle including (i) a quantum dot contributing to the photoelectric conversion and (ii) a material having a band gap larger than that of the quantum dot, the quantum dot being coated with the material; and a hole transport layer stacked on the first layer.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a photoelectric converting film stack type solid-state image pickup device fabricated by stacking a photoelectric converting film on a semiconductor substrate having formed on the surface thereof a signal read circuit. [0003] 2. Description of the Related Art [0004] As for the photoelectric converting film stack type solid-state image pickup device, a prototype device is described, for example, in JP-A-58-103165. In this solid-state image pickup device, three photosensitive layers are stacked on a semiconductor substrate, and electrical signals of red (R), green (G) and blue (B) detected by respective photosensitive layers are read out by MOS circuits formed on the semiconductor substrate surface. [0005] Solid-state image pickup devices having such a constitution were proposed in the past and thereafter, CCD-type image sensors or CMOS-type image sensors where a large number of light-...

AI Technical Summary

Benefits of technology

The present invention provides a photoelectric converting film stack type solid-state image pickup device that can efficiently take out photoelectric charges from the photoelectric converting film. The device includes a semiconductor substrate with a signal read circuit and at least one photoelectric converting film interposed between two electrode films. The photoelectric converting film consists of an ultrafine particle layer with a quantum dot and a material having a larger band gap, which helps to take out the signal charges. The hole transport layer stacked on the first layer can be made of an impurity-doped semiconductor or an organic film. The quantum dot can be made of CdSe or CdS, and the material coated on the quantum dot can be ZnSe or ZnS to prevent recombination of electron-hole pairs. The device can pick up color images with good color reproduction.

Problems solved by technology

However, CCD-type image sensors or CMOS-type image sensors are reaching the limit of their technical progress and come to encounter a problem of bad production yield because the opening size of one light-receiving part is about 2 μm and approximated to the wavelength order of incident light.

Furthermore, the upper limit of the quantity of photoelectric charges accumulated in one minute light-receiving part is as small as about 3,000 electrons and with this number of electrons, it is difficult to clearly express 256 gradations.

Therefore, CCD-type or CMOS-type image sensors can be hardly expected to be more enhanced in view of pictorial quality or sensitivity.

However, since the ultrafine particle used is silicon in both of Japanese Patent No. 3,405,099 and JP-A-2002-83946, an electron-hole pair generated upon receiving light cannot be satisfactorily prevented from recombining on the ultrafine particle surface and this causes a problem that the performance as a solid-state image pickup device is not satisfied.

In order to practically use the photoelectric converting film stack type solid-state image pickup device, what material is used to form the photoelectric converting film is present as a problem.

However, it is necessary to solve another problem that even when a CdSe quantum dot with an ZnS shell is merely dispersed in a medium and formed into a film and the film (photoelectric converting film) is interposed between upper and lower transparent electrode films and applied with a voltage, the photoelectric charges (signal charges) cannot be efficiently taken out.

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