Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Responsive to non-optical – non-electrical signal
Patent
1992-04-09
1994-01-25
Mintel, William
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Responsive to non-optical, non-electrical signal
257274, 257369, 257417, 257419, 73517R, 73517B, 73726, H01L 2966, H01L 2996, H01L 2984, H01L 2702
Patent
active
052818365
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the field of sensors using field effect semiconductor devices. It relates more particularly to a sensor for measuring a physical (i.e. non-electrical) property such as pressure, stress, deformation, temperature, etc. . . . , and constituted in the form of a ring oscillator using metal oxide semiconductor field effect transistors (MOSFETs).
BACKGROUND OF THE INVENTION
It has long been known that silicon, the base material from which MOSFETs are made, has piezoresistive properties that are of interest in the field of sensors.
Also known, e.g. from European patent EP-B-0 040 795, is a semiconductor sensor comprising an odd number of complementary metal oxide semiconductor (CMOS) inverters disposed in a zone which is sensitive to pressure, the inverters being inter connected to form a pressure sensitive ring oscillator. The frequency of the oscillator obtained in this way is directly related to the stress to which the semiconductor devices are subjected under the effect of pressure.
An object of the invention is thus to provide a semi conductor sensor having very good sensitivity while maintaining a relatively low cost price. Another object is to eliminate sensor drift under the effect of temperature and to improve the yield of the manufacturing process by reducing the number of rejects.
SUMMARY OF THE INVENTION
The sensor of the invention comprises a ring oscillator made up from an odd number of CMOS inverters disposed in a zone which is sensitive to the physical property which is to be measured; for each CMOS inverter, the N channel of the NMOS transistor is substantially perpendicular to the P channel of the PMOS transistor. This serves to increase sensor sensitivity by about 15% to 20% compared with a parallel disposition.
The sensitive zone may in particular take the form of a deformable membrane; in which case the physical property to be measured is pressure.
In various particular embodiments, the sensor comprises at least one pair of ring oscillators so as to reduce sensor drift related to temperature variations.
In a particularly advantageous embodiment, the sensitive zone of the sensor is provided with a plurality of ring oscillator pairs, thereby reducing the number of rejects during the manufacturing process.
In order to obtain more complete elimination of an interfering physical property such as temperature, the sensor may also be provided with at least one additional oscillator which is sensitive solely to said interfer physical property, thereby serving as a reference.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention are described by way of example with reference to the accompanying drawings, in which:
FIGS. 1A and 1B are respectively a plan view and a section view of a first embodiment constituting a pressure sensor;
FIGS. 2A and 2B are diagrams showing the piezoresistive coefficients of NMOS and PMOS transistors respectively;
FIG. 3 is a plan view of a second embodiment of a pressure sensor including a pair of ring oscillators; and
FIG. 4 is a plan view of a third embodiment comprising four pairs of ring oscillators.
DETAILED DESCRIPTION
The sensor of the invention is made from a wafer of silicon which includes a zone that is sensitive to the physical property to be measured. In the particular embodiments described below, this zone is constituted by a membrane which is sensitive to pressure. It will readily be understood that the sensitive zone could also be the surface of a simple beam and that the physical property to be measured could be stress or else deformation.
In a first embodiment shown in FIGS. 1A and 1B the silicon wafer 1 is oriented in the (100) plane and includes a rectangular pressure-sensitive membrane 2 with a ring oscillator 3 disposed in the center thereof. The oscillator 3 comprises an odd number of CMOS inverters, e.g. 89 inverters giving an oscillation frequency of about 1 MHz. For further details concerning a ring oscillator such as the oscillator 3, reference may be made in particular to Chapter 8 entitled "Analog Basic
REFERENCES:
patent: 3492861 (1970-02-01), Jund
patent: 3624315 (1971-11-01), Broce et al.
patent: 4894698 (1990-01-01), Hijikigawa et al.
patent: 4965697 (1990-10-01), Mosser et al.
patent: 5115292 (1992-05-01), Takebe et al.
Article by Neumeister et al., Jul. 1985, vol. 7, No. 3, Sensors and Actuators, pp. 167-175, "A Silicon Pressure Sensor Using MOS Ring Oscillators".
Mosser Vincent
Suski Jan
Gaudier Dale V.
Mintel William
Saadat Mahshid
Schlumberger Industries
LandOfFree
Semiconductor sensor with perpendicular N and P-channel MOSFET's does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor sensor with perpendicular N and P-channel MOSFET's, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor sensor with perpendicular N and P-channel MOSFET's will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-729826