Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – In combination with or also constituting light responsive...
Reexamination Certificate
2000-11-16
2003-02-11
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
In combination with or also constituting light responsive...
C257S080000, C257S415000, C257S419000, C257S428000, C257S431000, C257S447000
Reexamination Certificate
active
06518597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an infrared ray sensor of a low resistance and a high sensitivity, and a method for fabricating the same.
2. Background of the Related Art
In general, in the infrared ray (IR) sensor for sensing an emitted energy, there are photonic type sensors of photovoltaic effect or photoconductive effect, and thermal type sensors, such as bolometers, pyroelectric sensors, and thermopile sensors. The photonic type sensors, using an electric characteristic change of a sensor coming from exited electrons caused by an incident radiation, has an excellent sensing capability and a fast responsibility, within a selected wavelength range. However, the photonic type sensors has process technologies which have not yet been established fully, are expensive, and operative below a liquid-N
2
temperature. Recently, thermal type sensors which can be used commercially, and industrially are developed. The thermal type sensor requires no cooling, and are inexpensive, and reliable, and provides usefull information on bodies which can not be known by means of a visible image. The thermal type sensors has applications in fields of production examination, process monitoring, non-contact, non-destructive testing, and the like. However, even the thermal type sensors, not only have process technologies which have not yet been matured fully, but also have a high cost of substrate and uniformity which are problems to be solved. Consequently, the thermopile sensors are under active study, which can resolve the above problems, and fabrication of which is possible by using an available semiconductor fabrication process. The thermopile sensor uses the Seebeck effect in which a thermoelectric power is generated in proportion to a temperature difference if there is the temperature difference between one sides of two different conductors or semiconductors which are in contact and the other sides thereof which are opened, which can be expressed as an equation shown below.
V
AB
=
N
∫
T
A
T
H
(
a
A
-
a
B
)
ⅆ
T
Where, a
A
and a
B
denote Seebeck coefficients of the two materials in the thermopile, T
A
and T
B
denote temperatures of contact portions and opened portions of the materials, and N is a number of couples connected. As can be known from the equation, what are required for greater output of the sensor are a greater difference of Seebeck coefficients of the two materials, a greater temperature difference between the contact portion and the opened portion, and many numbers of the couples. As shown in FIGS.
1
~
4
, for satisfying those conditions, an array in which thermocouples are connected in series are fabricated, each formed of different materials having great thermoelectric powers and opposite polarities, disposed in a hot region and a cold region insulated from the hot region, alternately. In general, the cold region is disposed on a massive support for an effective heat sink. That is, the thermopile is two different thermoelectric materials disposed on a thin diaphragm having a low thermal conductance and a low thermal capacitance. Such a structure can enhance a performance of a detector and permits to reduce cost per a detector by means of a batch fabrication. Thin film thermopiles are used in various fields, and are the most general detectors used in IR spectrometers, presently. In summary, of the conditions for enhancing sensor outputs, it is difficult to control the second and third conditions as they are significantly influenced from a structure and a size of the thermocouples. And, meeting the first condition requires selection of appropriate materials. Thermoelectric materials for use in thermopiles are required to have a high electric conductivity for reducing a thermal noise and minimizing a Joule's heat loss, and a low thermal conductivity for minimizing a thermal conduction between the hot junction and the cold junction. However, such problems can not be coexistence, and a relation defined as Z=&sgr;a
2
/k is used in selection of an appropriate material for fabrication of the thermopiles. The above equation is not so advantageous for metals with small Seebeck coefficients. A heavily-doped semiconductor has a high ‘Z’ value, and therefore, is an optimal thermoelectric material. The semiconductor has a relationship between the doping concentration and the Seebeck coefficient. That is, though a heavy doping is required for dropping an internal resistance of the sensor, the heavier the doping, the smaller the Seebeck coefficient. Therefore, an optimal condition should be fixed taking the Seebeck coefficient and the sensor internal resistance into account on the same time. And, one another matter to take into account in selection of the thermoelectric material for use in fabrication of the thermopile is selection of a thermoelectric material suitable for mass production. That is, great Seebeck coefficients of the two materials can not be only condition for selecting as the thermoelectric materials for the thermopile. Thermoelectric materials used widely currently in this reason is a doped polysilicon and aluminum. As those materials are used in CMOS fabrication process, in fabrication of the thermopile sensor, an existing CMOS mass production process can be used as it is. In such a thermopile sensor, a black-body formed close to a hot junction of an IR sensor absorbs an incident infrared ray, and a temperature component in the cold junction portion is heat sunk through silicon, to cause a temperature difference between the hot junction and the cold junction, that excites an electromotive force.
However, referring to
FIG. 2
, the related art thermocouple sensor having a resistance of a first thermocouple material of a semiconductor and a resistance of a second thermocouple material of a metal connected in series, which form an equivalent circuit, has a substantially great internal resistance owing to the resistance of the semiconductor. In noise components affecting operation of the related art thermopile sensor, there are a thermal coupling which is a thermal noise coming from an environment, a radiative coupling which is a noise coming from environmental infrared ray emission, and an electrical noise occurred when an application circuit is formed. The thermal coupling and the radiative coupling, components coming from a sensor operative environment, are not easy to solve. However, the electrical noise has a Jhonson noise expressed as the following equation as a major electrical noise source because the electrical noise has major impedance component of the thermopile sensor as a resistance component.
V
J
=(4
kTRB
)
½
,
where, V
j
denotes a Jhonson Noise voltage, k denotes the Boltzmann constant(1.38×10
−23
J/K), T denotes an absolute temperature constant K, R denotes a device resistance, and B denotes a nosie bandwidth. Therefore, as can be known from the above equation, it is required to reduce the internal resistance of the sensor for reducing the noise.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an infrared ray sensor and a method for fabricating the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an infrared ray sensor and a method for fabricating the same, which can reduce an internal resistance of the sensor and maintain a high sensitivity.
Another object of the present invention is to provide an infrared ray sensor and a method for fabricating the same, which can improve a thermal noise and enhance a yield.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appen
Fleshner & Kim LLP
Flynn Nathan J.
Forde Remmon R.
LG Electronics Inc.
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