Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
1998-12-29
2001-01-09
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C438S051000, C438S739000, C251S315040
Reexamination Certificate
active
06171879
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of integrated circuits, and, more particularly, to an integrated circuit and method having the capability of sensing activity.
BACKGROUND OF THE INVENTION
Over the years, various microelectromechanical systems (“MEMS”) have arisen which require the necessity to sense temperature, pressure, strain, acceleration, rotation, infrared radiation, chemical properties of liquids and gases, and other physical inputs. Accordingly, various types of microsensors have been developed which receive analog and digital electrical inputs and also sense or measure these other physical inputs, e.g., acceleration, pressure, temperature, strain.
Integrated circuits are widely used in many of these MEMS or electronic applications. Various integrated circuit manufacturing processes, e.g., very large scale integrated (“VLSI”), are also widely known and provide various advantages. The complimentary metal oxide semiconductor (“CMOS”) manufacturing technology, for example, generally provides a low power dissipation advantage over known metal oxide semiconductor (“MOS”) processes. Microsensor manufacturing which is compatible with known integrated circuit manufacturing processes, however, can be quite complicated, especially because of a need for integrating various types of structures at relatively low cost.
Some types of well known thermosensors, for example, are thermistors and thermocouples for measuring the temperature of a surrounding environment. Thermistors and resistive temperature detectors (“RTDs”) are primarily based on the concept of change of mobility and carrier density with temperature. These changes are often represented by temperature coefficients that may be constants or nonlinear functions of temperature. Because resistance of a thermistor is generally an exponential function, linearization networks are often used to make the output of a thermistor a linear function over a desired range. These linearization networks, however, often require the sacrifice of sensitivity.
A thermocouple, on the other hand, is generally based on a thermoelectric effect known as the Seebeck effect. Two different metals are usually joined at one point to form a thermocouple. Various metals, for example, can be used for various temperature ranges and sensitivity. Semiconductors can also be used with a metal to form a microthermocouple. The two materials are conventionally joined together at one end, e.g., a sensing junction, and terminated at their other ends in such a manner that the terminals, e.g., a reference junction, are both at the same and known temperature, e.g., a reference temperature. The leads from the reference junction are connected to a load resistance to complete the thermocouple circuit. Due to the Seebeck effect, a current is caused to flow through the circuit whenever the sensing junction and the reference junction are at different temperatures. Often in practice, for example, the reference junction is either held at a known constant temperature or is electrically compensated for variations in a preselected temperature.
Both the thermistor and the thermocouple, however, produce analog outputs which often are not readily compatible with associated detection circuitry or logic circuitry. Also, processing or detecting circuitry can increase overhead and costs associated with producing a microsensor, and especially an integrated sensor.
SUMMARY OF THE INVENTION
With the foregoing in mind, the present invention advantageously provides an integrated CMOS sensor and associated methods for sensing temperature variations in a surrounding environment. The present invention also advantageously provides an integrated sensor that is readily compatible with existing integrated circuit manufacturing technology and manufacturing processes, that has greater tolerance for small critical dimensions, and that provides better signal indication when interfacing with logic of an integrated circuit. The present invention additionally provides a cost effective method of forming an integrated sensor for sensing activity desired to be sensed, such as temperature variation in a surrounding environment or ambient environment.
More particularly, the integrated sensor preferably includes a switch detecting circuit.region and a sensor switching region connected to and positioned adjacent the switch detecting circuit region. The switch detecting circuit region is preferably provided by a CMOS switch detecting circuit region, such as an inverter circuit. The sensor switching region preferably includes a fixed contact layer, a sacrificial layer on the fixed contact layer, and a floating contact on the remaining portions of the sacrificial layer and overlying the fixed contact layer in spaced relation therefrom when in an open switch position. The floating contact also preferably extends lengthwise generally transverse to a predetermined direction. The floating contact is preferably formed of at least two layers of material, e.g., upper and lower layers, that have different thermal expansion coefficients so that the floating contact displaces in the predetermined direction responsive to a predetermined temperature variation and the difference in coefficients. The floating contact preferably then contacts the fixed contact layer responsive to sensing of the predetermined temperature variation so as to form a closed switch position. The switch detecting circuit region, for example, advantageously can then generate a signal responsive to the contact of the floating contact with the fixed contact layer, the separation of the floating contact from the fixed contact layer, or both the contact and the separation of the floating contact with the fixed contact layer.
According to a first embodiment of the present invention, the floating contact defines a released cantilever beam. This release cantilever configuration, for example, preferably has a sacrificial layer positioned between a first conducting layer defining the fixed contact layer and a second conducting layer defining the floating contact. At least unwanted portions of the sacrificial layer are removed so that the floating contact has only one support at an end thereof defined by the remaining portions of the sacrificial layer and thereby defining a released cantilever beam configuration directly overlying the fixed contact layer.
According to a second embodiment of the present invention, the floating contact is a released beam overlying the fixed contact layer and having a configuration which includes a plurality of supports. The plurality of supports, for example, can be a double support configuration which is also formed by having a sacrificial layer positioned between a first conducting layer defining the fixed contact layer and a second conducting layer defining the floating contact. At least unwanted portions of the sacrificial layer are removed, e.g., forming a window, so that the floating contact has at least two supports, e.g., on opposing ends and defined by the remaining portions of sacrificial layer, for the floating contact and thereby defines a double support released beam configuration.
According to other aspects of the present invention, the released beam of the sensor switching region of the integrated sensor preferably extends outwardly from the switch detecting circuit region a first predetermined length. The fixed contact layer extends outwardly from the switch detecting circuit region a second predetermined length. The second predetermined length is preferably greater than the first predetermined length so that the released beam readily contacts the fixed contact layer responsive to a temperature variation.
An integrated sensor according to the present invention preferably further includes temperature calibrating means associated with the released beam for providing a calibrated predetermined temperature sensed by the integrated sensor. The temperature calibrating means preferably includes a predetermined length of the released beam so as to substantially correspond to a selected temper
Chan Tsiu Chiu
DeSilva Melvin Joseph
Galanthay Theodore E.
Jorgenson Lisa K.
Niebling John F.
Regan Christopher F.
Simkovic Viktor
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