Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Responsive to non-optical – non-electrical signal
Reexamination Certificate
1998-12-21
2001-04-17
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Responsive to non-optical, non-electrical signal
C257S254000, C257S414000, C257S415000, C438S052000, C438S054000, C073S723000, C073S727000, C073S514160, C204S430000, C204S431000
Reexamination Certificate
active
06218687
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains generally to electronic/chemical/biological sensors. More particularly, the present invention pertains to electronic/chemical/biological microsensors which are capable of reliable operation at elevated temperatures of at least three hundred degrees Centigrade and most likely up to approximately five hundred degrees Centigrade. The present invention is particularly, but not exclusively useful as a microsensor with associated electronics which can be mounted on a so-called silicon-on-insulator substrate in either monolithic or hybrid configurations.
BACKGROUND OF THE INVENTION
The use of silicon as a substrate for integrated circuits and other high technology electronics is well known and has been an acceptable manufacturing material for many years. Specifically, it is well known that silicon lends itself to plasma etching and deposition processes as well as many other well known application techniques which are useful and necessary for the manufacture of miniaturized electronic circuitry. Further, it is also well known that although silicon is capable of operating in elevated temperature environments, it also happens that the performance of a silicon device is significantly degraded at elevated temperatures. For example, to name but a few, it is known that at elevated temperatures silicon will exhibit lower mobility, lower transconductance, higher power consumption, lower threshold voltage, higher junction leakage current and higher metal line resistance. In turn, these problems lead to excess power consumption, degradation of logic levels in electronic components, and degraded noise margin. Further, at elevated temperatures, silicon is also susceptible to what is commonly referred to in the industry as “cross-talk” (i.e. interference that is caused by energy from one signal invading another circuit by electrostatic or electromagnetic coupling). Obviously, the problems set forth above that are directly associated with operation in elevated temperature environments are to be avoided. This is so due to the fact many environments are susceptible to elevated temperatures and need to be effectively monitored. Damage control in ships, aircraft, trains and buildings is a prime example of the need for such monitoring.
It is known that many of the problems which are associated with electronic/chemical/biological sensors can either be minimized or entirely eliminated, if a proper substrate is chosen. The selection of a proper substrate material, however, requires more than the ability of the substrate to tolerate high temperatures. Clearly, many materials which have excellent tolerance of elevated temperatures do not have the other qualities which are necessary for their use as a substrate for electronic circuits. As indicated above, despite recognized shortcomings, silicon has very good operating characteristics and, as also indicated above, silicon is a material which has been widely used in the fabrication of many different electronic circuitry devices. With all of the above in mind, it has been recognized that silicon can still be used, and its susceptibility to diminished performance at elevated temperatures can be minimized, by mounting sensors and their associated electronic circuitry on very thin layers of silicon. Specifically, recent processes have been developed which allow for the fabrication of nearly pure silicon layers that are on the order of only about one thousand to two thousand angstroms in thickness.
In light of the above it is an object of the present invention to provide a microsensor with associated electronics for identifying changes in the magnitude of an environmental characteristic (e.g. temperature, gas concentration, and pressure) when the temperature of the environment is up to as high as in a range of three hundred to five hundred degrees centigrade. Another object of the present invention is to provide a microsensor with associated electronics which will accurately interpret changes in environmental characteristics that occur at elevated temperatures. It is another object of the present invention to provide a microsensor for identifying a change in an environmental characteristic which can do so with minimal power loss, minimal current leakage and minimal cross-talk. Still another object of the present invention is to provide a high temperature active microsensor which incorporates electronic circuitry that can be manufactured using standard manufacturing processes. Another object of the present invention is to provide a microsensor for identifying a change in an environmental characteristic at a temperature up to approximately three or five hundred degrees Centigrade which is simple to use, relatively easy to manufacture, and comparatively cost effective.
SUMMARY OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, a high temperature “smart” microsensor for identifying changes of environmental characteristics in an environment is provided. For purposes of the present invention, the descriptor “smart” shall be taken to mean that the sensor is associated with electronics which will record, evaluate and interpret the signal(s) which are generated by the sensor element(s). Importantly, the sensor element and its associated electronics are intended to be capable of providing information and initiating responsive actions which are necessary for reacting to an elevated temperature environment.
In detail, a “smart” microsensor in accordance with the present invention includes an insulated substrate. Specifically, for the microsensor of the present invention this insulated substrate includes a substantially flat insulator layer that is sandwiched between a base layer and a support layer. Importantly, the support layer, which is integrally attached to the top side of the insulator layer, has a thickness that is, preferably, in the range of about one thousand to two thousand angstroms. On the other hand, the thickness of the insulator layer will be on the order of about four thousand angstroms. The base layer, which is integrally attached to the bottom side of the insulator layer (i.e. on the side of the insulator layer that is opposite the support layer) can be considerably thicker than either the support layer or the insulator layer and is intended to provide a structural base for the complete device. Preferably, the base layer and the support layer are both made of silicon while the insulator layer, which is located between these two layers, is made of an oxide, such as silicon oxide (SiO
2
).
For the operational components of the present invention, a sensor element is mounted on the exposed surface of the support layer of the insulated substrate. For one embodiment of the present invention, the sensor element can be mounted along with the an electronic element (e.g. microprocessor) on the support layer to create a monolithic device. Alternatively, a sensor element and its associated electronics can be mounted on separate substrates to create a hybrid device. As contemplated for the present invention, the sensor element may be any of several types well known in the pertinent art, and may include electronic sensors, chemical sensors, or biological sensors, as well as sensors specifically designed to detect temperature or pressure. For example, sensor elements suitable for use with the present invention may be devices such as Metal Oxide Semiconductor Field Effect Transistors (MOSFET), ChemFETs, ceramic metallic cells (Cermets), strain gauges, or semiconductor devices such as ring oscillators.
Common to all of the sensor elements that may be used for the present invention is the fact that at least one electronic element is associated with the sensor element. Specifically, this electronic element is designed to receive a signal(s) from the sensor element that is indicative of a change in the environment that is being monitored. The electronic element will then evaluate the signal (perhaps together with signals received from other sensors) and interpret the signal(s). In this respect, the combi
General Atomics
Mintel William
Nydegger & Associates
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