There are many kinds of semiconductor sensors which have many uses. In particular, semiconductor sensors are widely used in imaging technologies such as video cameras, digital cameras, and optical navigation devices. Silicon is one example of a semiconductor that is widely used in such semiconductor sensors.
The responsivity of a semiconductor to incident light peaks in the visible light region, and decreases as wavelength increases in the infrared light region. This decrease in responsivity is accompanied by an increase in absorption depth—the longer the wavelength, the more deeply the light penetrates into the semiconductor before being absorbed. This generates both optical and electronic crosstalk.
FIG. 1 shows a portion of a semiconductor sensor 10 that includes three pixels 12, 14, and 16. The semiconductor sensor 10 may be a CMOS sensor, a CCD sensor, a v Maicovicon sensor (a trademark of Matsushita Electric Industrial Co., Ltd.), a contact sensor, or any other kind of semiconductor sensor. The basic structural details of such semiconductor sensors are known in the art, and thus are not shown in FIG. 1 for the sake of simplicity.
Ideally, a photon 18 of infrared light penetrating into the pixel 12 is absorbed in that same pixel 12 and generates an electron-hole pair consisting of an electron 20 and a hole 22 in a region of the pixel 12 where the electron 20 can be collected by a charge collecting structure of the pixel 12. Such a charge collecting structure is known in the art, and thus is not shown in FIG. 1 for the sake of simplicity.
However, a photon 24 of infrared light penetrating into the pixel 12 at a high angle of incidence relative to a normal to the surface of the pixel 12 may pass through the pixel 12 without being absorbed, and penetrate into the neighboring pixel 14 where it is absorbed and generates an electron-hole pair consisting of an electron 26 and a hole 28 in a region of the pixel 14 where the electron 26 can be collected by a charge collecting structure of the pixel 14. Such a charge collecting structure is known in the art, and thus is not shown in FIG. 1 for the sake of simplicity. This distorts the values of pixel light detection currents generated in the pixels 12 and 14, making the pixel light detection current generated in the pixel 12 smaller than it should be, and making the pixel light detection current generated in the pixel 14 larger than it should be.
This phenomenon is called optical crosstalk, and can be reduced by restricting the angles of incidence at which photons are incident on the semiconductor sensor 10 to angles of incidence near the normal to the semiconductor sensor 10. However, this typically requires one or more additional optical components, such as a collimating lens provided in front of the semiconductor sensor 10, and thus undesirably increases the cost, complexity, and size of the semiconductor sensor 10.
Furthermore, a photon 30 of infrared light may penetrate deeply into the pixel 12 before being absorbed and generating an electron-hole pair consisting of an electron 32 and a hole 34 in a region of the pixel 12 where the electron 34 cannot be collected by the charge collecting structure of the pixel 12. Instead, the electron 34 may diffuse into the neighboring pixel 16 where it may or may not be collected by a charge collecting structure of the pixel 16. Such a charge collecting is known in the art, and thus is not shown in FIG. 1 for the sake of simplicity. This distorts the light detection current generated in the pixel 12 and possibly the light detection current generated in the pixel 16, making the light detection current generated in the pixel 12 smaller than it should be, and making the light detection current generated in the pixel 16 larger than it should be if the electron 34 is collected by the charge collecting structure of the pixel 16.
This phenomenon is called electronic crosstalk, and is particularly severe in semiconductor sensors used to detect infrared light. Silicon sensors are particularly susceptible to electronic crosstalk. It is difficult to reduce electronic crosstalk, and no truly effective way of doing so has been known in the art, particularly with respect to electronic crosstalk generated by photons penetrating into the deepest parts of a pixel.