Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
1999-05-13
2001-09-04
Williams, Alexander O. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C257S467000, C310S330000, C310S332000, C315S327000, C315S22700A, C331S040000, C331S042000, C331S165000, C331S128000, C331S051000, C331S10700G, C334S030000
Reexamination Certificate
active
06285063
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a resonant circuit, particularly for a monolithic integration in electronic circuits.
High-quality filters and oscillators having low phase noise, which in turn require resonant circuits with high quality, are required for constructing highly selective reception or, respectively, transmission circuits, for example for use in radio communication systems. Increasing miniaturization in electronics means that filters and oscillators must also be available in a suitable size, i.e. in the size of integrated circuits. According to the prior art, such high-quality resonant circuits are realized as discrete elements, for example in the form of surface wave filters or quartz resonators. A complete integratability of these elements in electronic circuits is not possible without further ado because of different substrate materials, as a result whereof these solutions have the disadvantage of a high space requirement and of an increased cost expenditure in manufacture. Electrical resonant circuits, by contrast, can be completely integrated but exhibit the disadvantage of having only low quality that, in particular, is not adequate for application in radio communication systems.
Thge prior art of H. Lobensommer, “Handbuch der modernen Funktechnik”, Franzis-Verlag, Poing, 1995, pages 80 through 90, discloses monolithic quartz resonators and surface wave filters. What monolithic means, given quartz resonators, is that the function of a plurality of discrete elements (discrete resonators) is realized on one quartz substrate. The electrode pairs are arranged and dimensioned such on the substrate that the resonance can only form in limited zones. A coupling ridge that determines the respective coupling factor forms between the electrodes. The oscillatory amplitude decreases exponentially outside these zones. The discrete elements or discrete resonators are acoustically connected to one another via the oscillatory energy that is coupled out. Monolithic quartz resonators are manufactured for frequencies of into the range of approximately 100 MHZ. Surface wave filters are manufactured in such a way that a metal layer is vapor-deposited on a single-crystal, piezoelectric substrate and the structure and interdigital transducer is produces with a photo etching technology. Interdigital transducers are comb-like or, respectively, finger-like structures that engage into one another and whose fingers thereby overlap. These structures can comprise more than
100
fingers and respectively form a piezoelectric transducer that can generate and receive surface waves on the substrate.
The publications of T. W. Kenny et al in Appl. Phys. Lett. 58, 100 through 102 (1991) and in J. Vac. Sci. Technol. A 10 (4), 2114 through 2118 (1992) disclose tunnel effect acceleration sensors wherein self-supporting beams or rectangles resiliently anchored due to under-etching are applied on silicon. An excursion of the resilient part as a consequence of forces of inertia given accelerations can be detected with the sensors. These sensors are manufactured by under-etching at the surface of a compact silicon block. European reference EP 0 619 494 discloses a tunnel effect acceleration sensor wherein the manufacture ensues in process steps of micromechanics that are compatible with the technology for manufacturing integrated circuits. This method of manufacture has the advantage that a following electronic circuit can be integrated in the silicon substrate together with the sensor and precision and signal-to-noise ratio of the sensor can thus be significantly improved.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a resonant circuit that avoids the disadvantages of the resonant circuits of the prior art.
According to the present invention, the resonant circuit has at least one resonant body of semiconductor material anchored on the surface of a semiconductor substrate, at least one first electrode being arranged on the semiconductor material. Further, the resonant circuit has at least one second electrode, whereby the first and second electrode are arranged lying opposite one another. Given application of an AC-superimposed DC voltage between the first and the second electrode, the resonant body is excited to a mechanical oscillation by the superimposed alternating voltage. The coupling between the mechanical oscillation of the resonant body and the electrical oscillation thereby ensues by electrostatic or, respectively, magnetic forces. This inventive realization has the advantage that the resonant body can be monolithically produced on or, respectively, in the semiconductor substrate with micromechanical methods, and a complete integration in electrical circuits is thus enabled given little economic outlay.
According to developments of the present invention, the electrodes can be realized by an electrically conductive doping or by a metallization. As a result of the applied AC voltage, a static electrical field arises between the electrodes, this producing an electrostatic capacitance. The AC voltage superimposed on the DC voltage effects a change of the electrical field and, thus, of the electrostatic forces acting on the beam, whereby the change of the forces causes an excursion of the resonant body. Depending on the geometrical dimensions and on the semiconductor material employed, the resonant body has a mechanical resonant frequency at which it resonates given a correspondingly dimensioned AC voltage. The mechanical resonant frequency of the resonant body in a further development can be varied by heating, whereby the heating can be produced by a flow of current through the first electrode. The electrical equivalent circuit of the resonant circuit essentially corresponds to that of a quartz resonator.
In conformity with first embodiments of the present invention, the resonant body is configured as a bendably anchored beam that is preferably arranged in a cavity in the semiconductor substrate or on the surface of the semiconductor substrate, or as a membrane that is arranged over a cavity in the semiconductor substrate. In particular, the bendably anchored beam has the advantage of a simple manufacture on the basis of known micromechanical manufacturing methods. According to further developments of the present invention, the second electrode is arranged on the semiconductor substrate or on a further bendably anchored beam. The after embodiment advantageously enables a higher efficiency of the resonant circuit since a greater mechanical mass is placed into motion with given electrostatic or, respectively, magnetic forces. Moreover, the further beam can be manufactured in the same way or, respectively, in the same work steps as the beam on which the first electrode is arranged.
In further developments, the resonant body is arranged in a cavity that is formed by a semiconductor layer additionally applied on the semiconductor substrate. The first electrode at the resonant body and the second electrode at the semiconductor layer are arranged lying opposite one another. This embodiment can simplify the manufacturing process for the resonant circuit, as well as, providing very good protection of the resonant body against environmental influences.
According to a further development, the semiconductor substrate and the semiconductor material are respectively based on silicon, gallium-arsenide or other semiconductor materials of the III-V group. This great selection of different semiconductor materials with which the resonant circuit can be realized enables a universal integration of the resonant circuit in the respectively existing semiconductor material, whereby the geometrical dimensions of the resonant body must be matched to the respective physical properties of the semiconductor material.
The inventive resonant circuit is especially advantageously utilized in an oscillator or band-pass filter of a Sigma-Delta transducer. These areas of employment require a high quality of the resonant circuit that is advantageously met by the resonant
Emmer Dieter
Splett Armin
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
Williams Alexander O.
LandOfFree
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