Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
2002-05-31
2004-10-19
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C250S214100, C257S448000
Reexamination Certificate
active
06806454
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to image sensors.
2. Description of the Related Art
A variety of modern electronic systems have created a strong demand for low-cost, high-quality, mega-pixel image sensors. In response to this demand, currently-available image sensors generally provide arrays of photodetectors (e.g., photogates or photodiodes) that are coupled to readout structures (e.g., charge-coupled-device (CCD) registers or complementary metal-oxide-semiconductor (CMOS) arrays). The photodetectors generate sense signals in response to incident electromagnetic radiation and the readout structures transport these sense signals to an image-sensor output port.
Currently-available image sensors are typically fabricated in accordance with very large-scale integration (VLSI) techniques. Accordingly, they take advantage of photolithographic processes which can define a large number of semiconductor devices on an underlying semiconductor substrate and also define a multiple-layer interconnect structure over the semiconductor devices to facilitate routing of signals and power among these devices.
Current image-sensor arrangements, however, create a significant conflict because different functional systems of the image sensor demand access through the same internal spaces of the VLSI structure. This conflict is exemplified in
FIG. 1
which illustrates a conventional image sensor
20
that carries photolithographically-generated semiconductor devices
22
on a (typically silicon) substrate
24
. Arranged over the semiconductor devices is a photolithographically-generated interconnect structure
26
that comprises alternating layers of interconnect lines and insulators.
The interconnect structure
26
connects a portion of the semiconductor devices
22
to form an array of photodetectors
28
which each receive focused electromagnetic radiation
30
from a respective one of an array of microlenses
32
that are positioned in the upper part of the image sensor. Although microlenses are not required in all image sensors, they are often used for increasing the percentage of electromagnetic radiation that falls upon the photodetector array.
The sensed signals generated by each of the photodetectors represents a respective pixel in a detected image and these sensed signals are routed to a sensor output port by a transmission system that is formed with the interconnect structure
26
and other portions of the semiconductor devices
22
.
From
FIG. 1
, it is apparent that the focused incident radiation
30
must pass through the interconnect structure
26
to impinge upon the photodetectors
28
. Due to various restraints (e.g., intrinsic properties of silicon and application-imposed boundary constraints), each pixel portion of radiation has asymptotically approached a current lateral dimension
34
on the order of 3 micrometers. In contrast, an exemplary 90 nanometer VLSI fabrication process can form something on the order of
100
semiconductor devices in the same area of the substrate
24
.
Accordingly, a substantial number of semiconductor devices and a significant portion of the interconnect lines are excluded from the regions of incident radiation
30
. This exclusion imposes a number of penalties (e.g., increased chip size, increased design and fabrication costs and decreased performance features) on the current image sensor art. Although concepts have been proposed (e.g., optically-transparent interconnect lines) to alleviate some of these penalties, they generally add other disadvantages (e.g., increased sensor cost).
SUMMARY OF THE INVENTION
The present invention is directed to image sensors that reduce conflicts between different sensor functions. Sensor embodiments of the invention include:
a) a substrate,
b) semiconductor devices and an interconnect structure carried over the substrate,
c) reference and sense electrodes and a photoconductive medium that are carried over the interconnect structure, and
d) vias that couple the reference and sense electrodes to the interconnect structure and semiconductor devices.
The semiconductor devices are thereby connectable by the interconnect structure to realize the functions of a signal conversion and transmission circuit without regard to the sense functions of the photoconductive medium and its associated reference and sense electrodes. Different sensor elements do not demand access through the same internal VLSI spaces and may thus be independently arranged to enhance their respective sensor functions. Coupling is realized by vias whose lateral extent is negligible and which may be laterally moved so long as they contact their intended target.
In addition, sensors of the invention are suitable for a wide variety of sensor applications because they will respond to radiation rays that are orthogonal to the sensor's upper face and also to radiation rays that are tilted from this relationship, and radiation that would otherwise be attenuated or scattered by passage through associated structures.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 5796433 (1998-08-01), Dyck
patent: 5886353 (1999-03-01), Spivey et al.
patent: 5907627 (1999-05-01), Borza
patent: 6100570 (2000-08-01), Saito
patent: 6300612 (2001-10-01), Yu
patent: 6320189 (2001-11-01), Ouvrier-Buffet et al.
patent: 6501142 (2002-12-01), Thomas et al.
Allen Stephone B.
Analog Devices Inc.
Koppel, Jacobs Patrick & Heybl
Lee Patrick J.
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