Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-03-16
2003-11-18
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S444000, C257S457000, C257S290000, C257S291000, C257S656000, C327S503000
Reexamination Certificate
active
06649993
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to PIN photo diode active pixel sensors. In particular, the present invention relates to an elevated PIN diode sensor with a simplified upper electrode contact structure.
2. Description of the Background
Image sensors such as charged coupled devices (CCDs) and active pixel sensors are used in a wide range of applications such as digital cameras, camcorders, and night vision enhancement systems. In these applications, light detected at an array of such image sensors is converted to electrical signals that have amplitudes proportional to the intensity of the light. Thus, the image sensors can convert an optical image into a set of electronic signals. The electronic signals may represent intensities of colors of light received by the image sensors. The electronic signals can be conditioned and sampled to allow image processing.
Integration of the image sensors with signal processing circuitry is becoming more important because integration enables miniaturization and simplification of imaging systems. Integration of image sensors along with analog and digital signal processing circuitry allows electronic imaging systems to be low cost, compact, and require low power consumption.
Historically, image sensors have predominantly been CCDs. CCDs are relatively small and can provide a high-fill factor. However, CCDs are very difficult to integrate with digital and analog circuitry. Furthermore, CCD systems dissipate large amounts of power and suffer from image smearing problems.
Active pixel sensors are an alternative to CCD sensors. Active pixel sensors can be fabricated using standard CMOS processes. Therefore, active pixel sensors can easily be integrated with digital and analog signal processing circuitry. Further, CMOS circuits dissipate small amounts of power.
FIG. 1
shows a cross-section of a prior art array of image sensors. This array of image sensors includes PIN diode sensors located over a substrate
10
. An interconnection structure
12
electrically connects an N-layer (N-type layer)
14
of the PIN diodes to the substrate
10
, such as a silicon substrate. An I-layer (intrinsic layer)
16
is formed over the N-layer
14
. A P-layer (P-type layer)
18
is formed over the I-layer
16
. The P-layer
18
, the I-layer
16
and the N-layer
14
form the array of PIN diode sensors. A first conductive via
20
electrically connects a first diode sensor to the substrate
10
, and a second conductive via
22
electrically connects a second diode sensor to the substrate
10
. A transparent conductive layer
24
is located over the array of diode sensors. A conductive lead
26
is connected to the transparent conductive layer
24
. The conductive lead
26
is connected to a bias voltage that allows biasing of the P-layer
18
of the array of PIN diode sensors to a selected voltage potential.
A limitation of the image sensor structure of
FIG. 1
is the electrical connection between the conductive lead
26
and the transparent conductive layer
24
. The transparent conductive layer
24
must be electrically conductive to allow biasing of the PIN diodes, and must be transparent to allow the PIN diodes to receive light. Generally, it is very difficult to bond to the types of materials that must be used to form the transparent conductive layer
24
. Therefore, the conductive lead
26
must be attached to the transparent conductive layer
24
with the aid of some type of clamp or support structure. The result is an electrical connection which is not reliable and which is expensive to produce.
It is desirable to have an active pixel sensor formed adjacent to a substrate in which a transparent conductor is reliably electrically connected to a pixel sensor bias voltage which originates on the substrate.
SUMMARY
An active pixel sensor is provided that includes a semiconductor substrate, an interconnection structure adjacent to the substrate, and a sensor interconnect structure adjacent to the interconnection structure. Photo sensors that contain individual pixel electrodes and an I-layer are formed over the sensor interconnect structure. A transparent conductor is deposited over both the photo sensors and an exposed conductive element in the interconnection structure. The conductive element passes through the interconnection structure to the substrate and allows a pixel sensor bias voltage that originates from circuitry within the substrate to be applied to the transparent conductor. A second conductive element in the interconnection layer is left exposed to allow connection to external packaging or other devices.
The substrate may contain active circuits to sense charge accumulation by the photo sensors due to the photo sensors receiving light. The photo sensors may include an additional P-layer formed between the I-layer and the transparent conductor, with the inner surface of the transparent conductor electrically connected to the P-layer, the I-layer, and the pixel interconnect layer.
In one embodiment, the semiconductor substrate contains a junction contact layer over which the interconnection structure has been removed. The transparent conductor is deposited over the photo sensors and the exposed junction contact layer in the substrate itself This allows a pixel sensor bias voltage that originates from circuitry within the substrate to be applied directly to the transparent conductor.
In one embodiment, the active pixel sensor is formed by forming the interconnection structure adjacent the substrate and the sensor interconnect structure adjacent the interconnection structure. At least one pixel electrode is formed adjacent the sensor interconnect structure and an I-layer is deposited over the at least one pixel electrode and pixel interconnect layer. A portion of the I-layer and pixel interconnect layer is removed to expose the conductive element. A transparent conductor is deposited over the I-layer and conductive element.
REFERENCES:
patent: 5408130 (1995-04-01), Woo et al.
patent: 6018187 (2000-01-01), Theil et al.
patent: 6051867 (2000-04-01), Theil et al.
patent: 6114739 (2000-09-01), Theil et al.
Agilent Technologie,s Inc.
Landau Matthew C
Lee Eddie
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