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  Thin-film transistors based on tunneling structures and applicationsUSPTO Application #: 20070120110Title: Thin-film transistors based on tunneling structures and applications Abstract: A hot electron transistor includes an emitter electrode, a base electrode, a collector electrode, and a first tunneling structure disposed and serving as a transport of electrons between the emitter and base electrodes. The first tunneling structure includes at least a first amorphous insulating layer and a different, second insulating layer such that the transport of electrons includes transport by means of tunneling. The transistor further includes a second tunneling structure disposed between the base and collector electrodes. The second tunneling structure serves as a transport of at least a portion of the previously mentioned electrons between the base and collector electrodes by means of ballistic transport such that the portion of the electrons is collected at the collector electrode. An associated method for reducing electron reflection at interfaces in a thin-film transistor is also disclosed. (end of abstract) Agent: Pritzkau Patent Group - Boulder, CO, US Inventors: Michael J. Estes, Blake J. Eliasson USPTO Applicaton #: 20070120110 - Class: 257025000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Thin Active Physical Layer Which Is (1) An Active Potential Well Layer Thin Enough To Establish Discrete Quantum Energy Levels Or (2) An Active Barrier Layer Thin Enough To Permit Quantum Mechanical Tunneling Or (3) An Active Layer Thin Enough To Permit Carrier Transmission With Substantially No Scattering (e.g., Superlattice Quantum Well, Or Ballistic Transport Device), Heterojunction, Quantum Well, Employing Resonant Tunneling The Patent Description & Claims data below is from USPTO Patent Application 20070120110. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present application is a continuation of copending application Ser. No. 11/113,587 filed on Apr. 25, 2005 which claims priority from U.S. provisional application 60/565,700 filed Apr. 26, 2004 and which also is a continuation-in-part of U.S. application Ser. No. 10/877,874 filed Jun. 26, 2004 and issued as U.S. Pat. No. 7,105,852 on Sep. 12, 2006; which is a continuation of application Ser. No. 10/347,534 filed Jan. 20, 2003 and issued as U.S. Pat. No. 6,756,649 issued Jun. 29, 2004; which is a continuation of Ser. No. 09/860,972 filed on May 21, 2001 and issued as U.S. Pat. No. 6,563,185 on May 13, 2003. BACKGROUND OF THE INVENTION [0002] The present invention relates generally to transistors and, more particularly, to transistors based on tunneling structures and their applications. [0003] Tunneling hot electron transistor amplifiers including a metal-insulator-metal-insulator-metal (M-I-M-I-M) configuration was first proposed by Mead in 1960.sup.1 and analyzed in detail by Heiblum in 1981..sup.2 Turning now to the drawings, wherein like components are indicated by like reference numbers throughout the various figures where possible, attention is immediately directed to FIG. 1, an exemplary M-I-M-I-M transistor of the prior art is illustrated. It is noted that the figures are not drawn to scale for purposes of clarity. [0004] FIG. 1 illustrates a partial cross sectional view of a typical M-I-M-I-M transistor, generally indicated by a reference numeral 100. M-I-M-I-M transistor 100 includes alternating single layers of metals and insulators, including an emitter electrode 110, a base electrode 112, a collector electrode 114, an emitter barrier 116, and a collector barrier 118. [0005] Other researchers have investigated similar transistor structures using epitaxial metal-insulator structures.sup.3, III-V semiconductor structures.sup.4a,4b, and structures using ferromagnetic metals.sup.4c and insulators.sup.4d. [0006] Additionally, in many circuit applications, it is advantageous to have complementary pairs of transistors such that one transistor turns on with positive base-emitter voltage and another, complementary, transistor turns on with negative base-emitter voltage. In this way, a push-pull amplifier or switch circuits may be built. Examples of such devices include silicon CMOS or bipolar push-pull power amplifiers, which use relatively low quiescent power. [0007] Prior art hot hole transistors.sup.8 have the same M-I-M-I-M as the previously described hot electron transistors. Device operation is also similar, with the exception that holes, instead of electrons, are the charge carriers in the device. However, the hot hole transistors of the prior art share the same problems as in prior art M-I-M-I-M hot electron transistors. [0008] As will be seen hereinafter, the present invention provides a remarkable improvement over the prior art as discussed above by virtue of its ability to provide fast thin-film devices with increased performance while resolving the aforedescribed problems present in the current state of the art. SUMMARY OF THE INVENTION [0009] As will be described in more detail hereinafter, there is disclosed herein a hot electron transistor adapted for receiving at least one input signal. The transistor includes an emitter electrode and a base electrode spaced apart from the emitter electrode such that at least a portion of the input signal may be applied across the emitter and base electrodes and, consequently, electrons are emitted from the emitter electrode toward the base electrode. The transistor also includes a first tunneling structure disposed between the emitter and base electrodes and configured to serve as a transport of electrons between and to the emitter and base electrodes. The first tunneling structure includes at least a first amorphous insulating layer and a different, second insulating layer disposed directly adjacent to and configured to cooperate with the first amorphous insulating layer such that the transport of electrons includes, at least in part, transport by means of tunneling. The transistor further includes a collector electrode, spaced apart from the base electrode, and a second tunneling structure between the base and collector electrodes. The second tunneling structure is configured to serve as a transport, between the base and collector electrodes, of at least a portion of the electrons emitted from the emitter electrode by means of ballistic transport such that the portion of the electrons is collected at the collector electrode. The input signal may include, for example, bias voltage, signal voltage, or electromagnetic radiation. [0010] In another aspect of the present invention, the transistor at least a selected one of the base and collector electrodes is formed, at least in part, of a semi-metal. Alternatively, a selected one of the base and collector electrodes is formed of a metal-silicide or a metal-nitride. [0011] In still another aspect of the invention, the second tunneling structure is configured to exhibit a first value of hot electron reflection, and wherein the second tunneling structure includes a shaped barrier energy band characteristic such that the first value of hot electron reflection is lower than a second value of hot electron reflection that would be exhibited by the second tunneling structure without the shaped barrier energy band characteristic. More specifically, the shaped barrier energy band characteristic includes a parabolic grading of the second tunneling structure. [0012] In another aspect of the invention, the transistor is configured to exhibit a first value of electron emission energy width, and wherein the first tunneling structure includes a shaped barrier energy band characteristic such that the first value of electron emission energy width is lower than a second value of electron emission energy width that would be exhibited by the transistor without the shaped barrier energy band characteristic. [0013] In yet another aspect of the invention, the emitter electrode is configured to exhibit a given Fermi level, and the first tunneling structure is configured to exhibit a given conduction band such that the given conduction band differs from the given Fermi level by less than 2 eV. [0014] In a further aspect of the invention, a hot hole transistor adapted for receiving at least one input signal is disclosed. The hot hole transistor includes an emitter electrode and a base electrode spaced apart from the emitter electrode such that at least a portion of the input signal may be applied across the emitter and base electrodes and, consequently, holes are emitted from the emitter electrode toward the base electrode. The hot hole transistor also includes a first tunneling structure disposed between the emitter and base electrodes, and configured to serve as a transport of holes between and to the emitter and base electrodes. The first tunneling structure includes at least a first amorphous insulating layer and a different, second insulating layer disposed directly adjacent to and configured to cooperate with the first amorphous insulating layer such that the transport of holes includes, at least in part, transport by means of tunneling. The hot hole transistor further includes a collector electrode spaced apart from the base electrode, and a second tunneling structure disposed between the base and collector electrodes and configured to serve as a transport, between the base and collector electrodes, of at least a portion of the hot holes emitted by the emitter electrode by means of ballistic transport such that the portion of the holes is collected by the collector electrode. [0015] In another aspect of the invention, a method for use in a hot electron transistor including a plurality of layer with a plurality of interfaces defined therebetween and ballistic electrons being transported therebetween is disclosed. The plurality of layers includes at least a first layer and a second layer adjacent and juxtaposed to each other and defining a first interface therebetween such that at least a portion of the ballistic electrons may be reflected at the first interface. The method for reducing electron reflection at least the first interface includes configuring the first layer to exhibit a first, selected wave function, and configuring the second layer to exhibit a second, selected wave function such that a first fraction of the ballistic electrons is reflected at the first interface. This first fraction is smaller than a second fraction of the ballistic electrons that would be reflected at the first interface without the second layer being configured to exhibit the second, selected wave function. [0016] In still another aspect of the invention, a transistor adapted for receiving at least one input signal is disclosed. The transistor includes an emitter electrode and a base electrode spaced apart from the emitter electrode such that at least a portion of the input signal may be applied across the emitter and base electrodes and, consequently, electrons are emitted from the emitter electrode toward the base electrode. The transistor also includes a first tunneling structure disposed between the emitter and base electrodes and configured to serve as a transport of electrons between and to the emitter and base electrodes. The transistor further includes a collector electrode spaced apart from the base electrode, and a second tunneling structure disposed between the base and collector electrodes, and configured to serve as a transport, between the base and collector electrodes, of at least a portion of the electrons emitted by the emitter electrode by means of ballistic transport such that the portion of the electrons is collectable at the collector electrode. The second tunneling structure is configured to exhibit a first value of hot electron reflection, and the second tunneling structure is further configured to exhibit a selected wave function such that the first value of hot electron reflection is lower than a second value of hot electron reflection that would be exhibited by the second tunneling structure without the selected wave function. [0017] In yet another aspect of the invention, a linear amplifier adapted for receiving at least one input signal is disclosed. The linear amplifier includes a hot electron transistor, which in turn includes a first emitter electrode and a first base electrode spaced apart from the first emitter electrode such that at least a first portion of the input signal may be applied across the first emitter and first base electrodes and, consequently, electrons are emitted from the first emitter electrode toward the first base electrode. The hot electron transistor also includes a first tunneling structure disposed between the first emitter and first base electrodes and configured to serve as a transport of electrons between and to the first emitter and first base electrodes. The first tunneling structure includes at least a first amorphous insulating layer and a different, second insulating layer disposed directly adjacent to and configured to cooperate with the first amorphous insulating layer such that the transport of electrons includes, at least in part, transport by means of tunneling. The hot electron transistor further includes a first collector electrode spaced apart from the first base electrode, and a second tunneling structure disposed between the first base and first collector electrodes and configured to serve as a transport, between the first base and first collector electrodes, of at least a portion of the electrons emitted from the first emitter electrode by means of ballistic transport such that the portion of the electrons is collectable at the first collector electrode. The linear amplifier also includes a hot hole transistor, which in turn includes a second emitter electrode and a second base electrode spaced apart from the second emitter electrode such that at least a second portion of the input signal may be applied across the second emitter and second base electrodes and, consequently, holes are emitted from the second emitter electrode toward the second base electrode. The hot hole transistor also includes a third tunneling structure disposed between the second emitter and second base electrodes and configured to serve as a transport of holes between and to the second emitter and second base electrodes. The third tunneling structure includes at least a third amorphous insulating layer and a different, fourth insulating layer disposed directly adjacent to and configured to cooperate with the third amorphous insulating layer such that the transport of holes includes, at least in part, transport by means of tunneling. The hot hole transistor further includes a second collector electrode spaced apart from the second base electrode, and a fourth tunneling structure disposed between the second base and second collector electrodes and configured to serve as a transport, between the second base and second collector electrodes, of at least a portion of the hot holes emitted by the second emitter electrode by means of ballistic transport such that the portion of the holes is collectable at the second collector electrode. In the linear amplifier, the hot electron transistor and the hot hole transistor are configured in a push-pull amplifier configuration. BRIEF DESCRIPTION OF THE DRAWINGS [0018] The present invention may be understood by reference to the following detailed description taken in conjunction with the drawings briefly described below. It is noted that, for purposes of illustrative clarity, certain elements in the drawings may not be drawn to scale. Furthermore, descriptive nomenclature such as, for example, vertical, horizontal and the like applied to the various figures is used for illustrative purposes only and is in no way intended as limiting useful orientations of the structure or device described. [0019] FIG. 1 is a diagrammatic view, in partial cross section, of a junction transistor device as disclosed in the aforementioned '185 patent. [0020] FIG. 2 is an energy band diagram corresponding to a hot electron transistor of the present invention. [0021] FIG. 3 is an energy band diagram corresponding to a hot hole transistor of the present invention. Continue reading... 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