WO2019020737A1 - Metal-based transistor comprising materials comprising at least one group iii element and one group v element. - Google Patents
Metal-based transistor comprising materials comprising at least one group iii element and one group v element. Download PDFInfo
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- WO2019020737A1 WO2019020737A1 PCT/EP2018/070274 EP2018070274W WO2019020737A1 WO 2019020737 A1 WO2019020737 A1 WO 2019020737A1 EP 2018070274 W EP2018070274 W EP 2018070274W WO 2019020737 A1 WO2019020737 A1 WO 2019020737A1
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- 239000002184 metal Substances 0.000 title claims abstract description 54
- 229910052751 metal Inorganic materials 0.000 title claims abstract description 54
- 239000000463 material Substances 0.000 title claims abstract description 48
- 229910021478 group 5 element Inorganic materials 0.000 title abstract 4
- 239000004065 semiconductor Substances 0.000 claims abstract description 39
- 239000007769 metal material Substances 0.000 claims abstract description 9
- 238000005036 potential barrier Methods 0.000 claims abstract description 9
- 239000000758 substrate Substances 0.000 claims abstract description 7
- 229910045601 alloy Inorganic materials 0.000 claims description 17
- 239000000956 alloy Substances 0.000 claims description 17
- 150000002736 metal compounds Chemical class 0.000 claims description 4
- 238000011084 recovery Methods 0.000 claims description 3
- 239000002019 doping agent Substances 0.000 abstract description 8
- 229910002601 GaN Inorganic materials 0.000 description 17
- 230000004888 barrier function Effects 0.000 description 12
- 230000000694 effects Effects 0.000 description 11
- 230000015556 catabolic process Effects 0.000 description 8
- 239000000243 solution Substances 0.000 description 7
- 230000008901 benefit Effects 0.000 description 6
- 229910019001 CoSi Inorganic materials 0.000 description 5
- 238000010586 diagram Methods 0.000 description 5
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 5
- 239000000969 carrier Substances 0.000 description 4
- 150000002739 metals Chemical class 0.000 description 4
- 229910001199 N alloy Inorganic materials 0.000 description 3
- 238000006731 degradation reaction Methods 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 238000004364 calculation method Methods 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 229910000807 Ga alloy Inorganic materials 0.000 description 1
- 229910001218 Gallium arsenide Inorganic materials 0.000 description 1
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 1
- YZCKVEUIGOORGS-UHFFFAOYSA-N Hydrogen atom Chemical compound [H] YZCKVEUIGOORGS-UHFFFAOYSA-N 0.000 description 1
- 229910000577 Silicon-germanium Inorganic materials 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
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- 230000005593 dissociations Effects 0.000 description 1
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- 230000001747 exhibiting effect Effects 0.000 description 1
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- 230000005669 field effect Effects 0.000 description 1
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- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000001451 molecular beam epitaxy Methods 0.000 description 1
- 230000004899 motility Effects 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 125000002524 organometallic group Chemical group 0.000 description 1
- 230000003071 parasitic effect Effects 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/76—Unipolar devices, e.g. field effect transistors
- H01L29/7606—Transistor-like structures, e.g. hot electron transistor [HET]; metal base transistor [MBT]
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/12—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed
- H01L29/20—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, only AIIIBV compounds
- H01L29/2003—Nitride compounds
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
- H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
- H01L29/66931—BJT-like unipolar transistors, e.g. hot electron transistors [HET], metal base transistors [MBT], resonant tunneling transistor [RTT], bulk barrier transistor [BBT], planar doped barrier transistor [PDBT], charge injection transistor [CHINT]
- H01L29/66939—BJT-like unipolar transistors, e.g. hot electron transistors [HET], metal base transistors [MBT], resonant tunneling transistor [RTT], bulk barrier transistor [BBT], planar doped barrier transistor [PDBT], charge injection transistor [CHINT] with an active layer made of a group 13/15 material
Definitions
- Metal-based transistor comprising materials comprising at least one element III and one element V
- the field of the invention is that of microwave components, aimed at producing microwave components that can reach cutoff frequencies up to THz.
- High Electron Mobility Transistor High Electron Mobility Transistor
- heterojunction bipolar transistors TH
- TBH heterojunction bipolar transistors
- MOCVD organometallic
- molecular jets ammonia. Indeed atomic hydrogen from the dissociation of the molecules allowing the growth of the GaN crystal associates with the doping atoms and prevents the electrical activation of the dopants. Electrical reactivation procedures are possible using thermal annealing but the thermal budget can be a factor of degradation of the quality of the heterostructures.
- the acceptor level is approximately 200 meV above the GaN valence band, which leads, even if the hydrogen removal stage operates correctly, to a weak electrical activation of the Mg dopants.
- the solubility limits of the dopants prevent exceeding unlimited concentrations, some 10 19 cm -3 for the Mg for example, the effective dopings are therefore close to 10 17 cm -3 leading to very high layer resistances (about 100 of kQ per square for thicknesses of 50 nm). These values are incompatible with a microwave operation since they would have to be much lower than the typical k ⁇ .
- the solid state components are essentially InP or Si (Ge) that allow operation up to 350GHz in the laboratory but for very low powers emitted. Solutions based on diodes exist but are difficult to adjust and historically difficult to integrate.
- the Applicant proposes a new power transistor based on materials III-V, with a vertical structure (weak surface effect), unipolar (for electrons to participate in electrical conduction), comprising a transmitter, a base and a collector, in which the base is metallic.
- the metal base is inserted into alloys of III-V materials, such as GaN alloys.
- the subject of the present invention is a transistor comprising a vertical structure comprising an emitter, a base, a collector characterized in that it comprises:
- a sub-collector comprising at least one layer made of a first semiconductor material comprising at least one element III and an n-doped element V with a first doping level;
- a collector comprising at least one layer made of a second semiconductor material comprising at least one element III and an n-doped element V with at least one second doping level, said at least one second doping level being lower than said first doping level;
- an emitter comprising at least one layer made of a third semiconductor material comprising at least one element III and an n-doped element V;
- a continuous metal base layer situated between the collector and the emitter and having a thinner thickness than the average ballistic path of the electrons in this metal, said metal base layer forming the base of the transistor and comprising a metallic material comprising minus the element N;
- the potential barrier ( ⁇ ⁇ ⁇ ) at the metallic material / third semiconductor material interface of the emitter is greater than the potential barrier ( ⁇ ) at the metallic material / semiconductor second material interface of the collector.
- the first and / or the second and / or the third semiconductor material is (are) an alloy of ln- x- y Al x Ga y N.
- the collector comprises at least one layer made of a second semiconductor material III-V ⁇ - ⁇ - ⁇ ⁇ . yAlx'Gay'N doped n with at least one second doping level, said at least one second doping level being lower than said first doping level and wherein the emitter comprises at least one layer made of a third semiconductor material III-V ln -xy AlxGa y N doped n.
- the first and / or the second and / or the third semiconductor material is (are) chosen from ScAIN or ScGaN.
- the collector may comprise different doping levels, or even within a layer.
- metal-based transistors can have cutoff frequencies exceeding the THz with high operating voltages (exceeding ten volts for such cutoff frequencies).
- the first semiconductor material of the sub-collector is GaN
- the second semiconductor material of the collector is GaN
- the third semiconductor material of the emitter is in or in ln 0, i 7 AI 0.83 or in
- the bandgap of the transmitter is greater than that of the base.
- the conduction band of the collector must ensure the absence of discontinuity unfavorable with that of the base (type 2 alignment, that is to say to avoid that a potential barrier is to be crossed by the electrons injected between the base and the collector) resulting in losses to the collection.
- the sub-collector and / or the collector and / or the emitter comprises (ennent) a multilayer structure or a gradual structure, allowing more favorable access or collection resistances.
- the base layer may advantageously comprise a metal having a crystalline mesh compatible with the alloys of gallium nitride chosen from and not exclusively: Nb 2 N, CrN, MoN, TaN.
- the metal base of the transistor of the invention is thus inserted into alloys of materials III-V, which requires that the selected metal compound be compatible with the epitaxial temperatures of said III-V materials and offers a compatible crystalline structure.
- the metal compounds based on nitride alloy offer for this reason a very good compatibility.
- the metal layer has a thickness less than or equal to 30 nanometers and preferably less than or equal to 10 nanometers.
- the transistor comprises at least one base recovery contact on the surface of the metal layer and at least one collector resumption contact on the surface of the sub-collector.
- At least the base-return contact on the surface of the metal layer and at least the collector-return contact on the surface of the sub-collector comprise a Ti layer and / or a substrate layer.
- the substrate is SiC or GaN or Si.
- the first n-type doping rate of the first semiconductor material belonging to the sub-collector is greater than or equal to 10 18 cm -3 .
- the second doping rate of the second semiconductor material belonging to the collector is of the order of 10 17 cm -3 , making it possible to reverse the appearance of the Kirk effect.
- parasitic effect of the transistor which consists in widening of the base area to the detriment of the collector area as a result of a high density of majority carrier injected from the base to the collector This effect is encountered in the normal operating mode of the transistor, at the collector base junction in reverse polarization, at a carrier injection threshold greater than the doping of the collector zone, a gradual erasure of the space charge area between the base and the collector is observed. widening of the base area thus leads to a decrease in the microwave gain of the transistor.
- FIG. 1 illustrates the conduction band diagram of a Si / CoSi 2 / Si metal-base transistor of the prior art
- FIG. 2 illustrates the block diagram of the conduction bands in a metal-based transistor based on
- FIG. 3 illustrates the evolution of the Schottky barrier height of nickel deposited on Al x Ga-i- x N alloys described in the literature
- FIG. 4 illustrates a sectional view of a metal-based transistor according to the invention.
- the transistor of the present invention takes advantage and high breakdown fields alloys of III-V materials such as ln xy AlxGa alloys are N and avoids surface effects difficult to control. It only uses majority carriers avoiding the catastrophic degradation effects specific to ambipolar components (TBH for Bipolar Strand to Heterojunction or HBT for "Heterojunction Bipolar Transistor", Laser) and is free from p-doping which has poor electrical conductivity, especially in high bandgap materials because of the intrinsic motility of the holes and the passivation effects of the hydrogen-bound dopants.
- TH Bipolar Strand to Heterojunction
- HBT Heterojunction Bipolar Transistor
- the metal base also avoids difficult ohmic contacting by using simple metal-metal junctions which have negligible contact resistances ( ⁇ . ⁇ instead of values between 0.1 ⁇ .mm and 1 Q.mm).
- the speed of the component is essentially fixed by the thickness of the epitaxial layers and not by the lateral dimension of patterns such as the gate in a field effect transistor. This makes it possible to reach microwave gain cut-off frequencies above 100 GHz by using size patterns greater than 500 nm allowing the use of optical l-line or even G-line optical steppers and not electronic masks. Steppers have the advantage of allowing much shorter exposure times than electronic masks, the difference being between minutes and hours.
- the solution of the present invention makes it possible to increase by an order of magnitude the available power densities. Even at lower frequencies, the present solution is of interest for the components based on ln -xy AlxGayN by greatly limiting the impact of surface phenomena (charges) and volume traps. It allows the improvement of low frequency noise and dispersive effects specific to planar components.
- the transistors of the present invention are said to be "Normally-off" (blocked if no voltages applied to the base). Due to this polarization mode, the power supply of the circuits may only include positive voltages, whereas the conventional HEMT solution requires two positive (drain) and negative (gate) power supplies. Being vertical, the components of the present invention avoid the surface effects encountered by current HEMT components.
- the transistors of the present invention are unipolar components that are less sensitive to catastrophic damage to conventional TBHs or lasers that are ambipolar.
- the metal layer simplifies the setting of the ohmic contacts on the base layer.
- the series resistances at the basic (or gate) control are a very sensitive point for the frequency rise of the components.
- the invention proposes to use the alloys of III-V materials such as ln xy AlxGayN alloys for making transistors metal base.
- III-V materials such as ln xy AlxGayN alloys for making transistors metal base.
- the alloys used of III-V materials such as GaN make it possible to produce asymmetric Schottky barriers ensuring the emission and collection of carriers.
- alloys of materials III-V it is possible to find metals having a good morphology even for thin, compatible such materials III-V.
- films of Nb 2 N in particular described in the article by David Meyer, Naval Research Laboratory, "Epitaxial Conductors: Metal Transition Nitride Development at NRL", WOCSEMMAD 2016, Arlington, AZ, USA and have a good morphology even for low thicknesses.
- These metal films have layer resistances of the order of 4 ohms per square for a thickness of 10 nm.
- Cutoff frequencies could be twice that of InP or SiGe TBHs, and the power density would be an order of magnitude larger.
- FIG. 2 illustrates, by way of example, a band diagram of a device according to the invention, comprising an emitter in ln 0, -i 7 AI 0.83 GaN, a base in Nb 2 N and a collector in GaN , highlighting that the potential barrier ⁇ ⁇ ⁇ at the metal / third semiconductor interface (corresponding to the base / emitter barrier) is greater than the potential barrier ⁇ ⁇ ⁇ at the metal / second semiconductor semiconductor interface (corresponding to the base / collector barrier).
- the arrows schematize the path of the electrons injected from the transmitter to the collector.
- the first and / or second and / or third semiconductor material is (are) an alloy of In xy AlxGayN.
- FIG. 3 shows, by way of example, the evolution of the Schottky barrier height with Al x Ga-i- x N alloys as a function of the concentration of aluminum for a Ni metal contact as described in the article: " Dependence of Ni / AIGaN Schottky barrier height on Al mole fraction ", Qiao Q, LS Yu, Lau SS, Redwing JM, JY Lin, and Jiang HX, Journal of Applied Physics 87, 801 (2000); doi: 10.1063 / 1 .371944.
- the emitter layer must have an aluminum concentration higher than that of the collector layer.
- the choice of metals best suited to the metal-based transistor structure of the invention if the use of III-V materials such as GaN alloys allows energy band engineering and collection much easier than for silicon components, it is necessary to obtain compatible metals GaN growth temperatures and having the good crystallinity allowing more precisely to obtain a heterostructure may be: I n - ⁇ X-YAI G y N / M cal / 1 1. No x - y Al x - N Gay.
- alloys Nb 2 N offer this type of physical properties with a mesh of 1% with SiC and therefore a compatibility with the crystalline mesh of GaN also.
- the Nb element has a high melting point of 2477 ° C.
- Thick Nb 2 N layers of 100 nm thickness currently have a layer resistance of 3.9 ohms per square. Very high 3.45eV barrier heights were measured with ⁇ .
- Other materials are also possible candidates such as: ScGaN, ScAIN, CrN, MoN, TaN.
- the electrons injected into the base pass through it in a ballistic manner. Only electrons that do not experience a collision can be collected.
- the free ballistic range in a metal has been studied for some metals. For CoSi 2 , it reaches 9nm, for Ag 27nm, for Au 22nm, for Pd 9nm and for Al 10nm.
- the construction rules of the components are similar to those of the TBH components except that the ohmic metal base contact is a metal / metal contact.
- FIG. 4 shows the diagram of a sectional view of an example of a transistor according to the invention:
- the metal-based transistor of the invention comprises: a substrate 100;
- a sub-collector 200 a collector 300;
- At least one collector contact 310 At least one collector contact 310
- the transistor structure of the present invention remains compatible thermal management solutions described in particular in the patent application EP 1276149 (Thomson-CSF, "semiconductor component with integrated heat sink", S. Delage, S. Cassette, H Blanck, E. Chartier, (1995), 95 08994, or the published French patent application 2,737,342, making it possible to envisage applications in the S or X band.
- the Applicant has carried out analytical calculations to evaluate the electrical performance of a metal-based transistor compared to those of a state-of-the-art heterojunction bipolar transistor and provided in the article by Zach Griffith, Kim YoungMin, Mattias Dahlstrom, Arthur C.
- the metal-based transistor has dimensions of 0.5 ⁇ x 7 ⁇ GaN identical to those of the THB InP transistor, with a metal base of Nb 2 N 3.5nm thick and the average free ballistic path is set at 20nm.
- Table 1 shows the values of the key parameters of the transistors. The parameters have been estimated on the basis of physical values available in the scientific literature and highlights the improvement in electrical performance expected with the metal-based transistor of the invention. It is important to mention that power gain cut-off frequencies greater than 1 THz would be accessible by increasing the thickness of the metal base to 6 nm, all other parameters being unchanged. The average free ballistic trajectory of the electrons injected into the metal base governs the current gain of the component and in the example given the gain in current would drop to 3.
Abstract
The subject matter of the invention is a transistor including a vertical structure comprising an emitter, a base, a collector characterized in that it comprises: - a substrate; - a subcollector including at least one layer made of a first semiconductor material comprising at least one group III element and one group V element that is n-doped at a first dopant density; - a connector including at least one layer made of a second semiconductor material comprising at least one group III element and one group V element that is n-doped at least a second dopant density, said at least second dopant density being lower than said first dopant density; -an emitter including at least one layer made of a third semiconductor material comprising at least one group III element and one n-doped group V element; - a continuous metal base layer, located between the collector and the emitter and the thickness of which is less than the mean ballistic path of electrons through this material, said metal base layer forming the base of the transistor and comprising a metal material including at least the element N; - the potential barrier (ΦBE) at the interface between the metal material and the third semiconductor material of the emitter is higher than the potential barrier (ΦBC) at the interface between the metal material and the second semiconductor material of the collector.
Description
Transistor à base métallique et comprenant des matériaux comprenant au moins un élément III et un élément V Metal-based transistor comprising materials comprising at least one element III and one element V
Le domaine de l'invention est celui des composants hyperfréquences, visant à réaliser des composants hyperfréquences pouvant atteindre des fréquences de coupure allant jusqu'au THz. The field of the invention is that of microwave components, aimed at producing microwave components that can reach cutoff frequencies up to THz.
Les composants GaN actuels utilisent essentiellement des composants horizontaux HEMT (High Electron Mobility Transistor) performants mais sensibles aux variations de charges en surface ainsi que dans le volume du semiconducteur. Current GaN components essentially use high performance horizontal HEMT (High Electron Mobility Transistor) components that are sensitive to surface charge variations as well as semiconductor volume.
Les composants verticaux tels que les transistors bipolaires à hétérojonction (TBH) à base par exemple de GaN ne sont pas de façon évidente des candidats possibles car le dopage de type P du GaN par Mg est très difficile, tout particulièrement si le matériau est épitaxié en phase vapeur aux organométalliques « MOCVD » ou voire même épitaxié par jets moléculaires ammoniac. En effet l'hydrogène atomique provenant de la dissociation des molécules permettant la croissance du cristal de GaN s'associe aux atomes dopants et empêche l'activation électrique des dopants. Des procédures de réactivation électrique sont possibles en utilisant des recuits thermiques mais le budget thermique peut être un facteur de dégradation de la qualité des hétérostructures. De surcroît le niveau accepteur est environ 200meV au-dessus de la bande de valence du GaN ce qui conduit, même si l'étape de suppression de l'hydrogène s'opère correctement, à une activation électrique faible des dopants Mg. Ainsi seulement quelques pour cents des atomes dopants physiquement présents contribuent vraiment au dopage actif du semiconducteur. Comme les limites de solubilité des dopants empêchent d'excéder des concentrations illimitées, quelques 1019 cm"3 pour le Mg par exemple, les dopages effectifs sont donc proches de 1017 cm"3 conduisant à des résistances de couche très élevées (une centaine de kQ par carré pour des épaisseurs de 50 nm). Ces valeurs sont incompatibles d'un fonctionnement hyperfréquence puisqu'il faudrait qu'elles soient bien inférieures au kQ typiquement. Vertical components such as heterojunction bipolar transistors (TBH) based for example on GaN are obviously not possible candidates because Ga-type doping of GaN by Mg is very difficult, especially if the material is epitaxially grown. Vapor phase with organometallic "MOCVD" or even epitaxied by molecular jets ammonia. Indeed atomic hydrogen from the dissociation of the molecules allowing the growth of the GaN crystal associates with the doping atoms and prevents the electrical activation of the dopants. Electrical reactivation procedures are possible using thermal annealing but the thermal budget can be a factor of degradation of the quality of the heterostructures. In addition, the acceptor level is approximately 200 meV above the GaN valence band, which leads, even if the hydrogen removal stage operates correctly, to a weak electrical activation of the Mg dopants. Thus only a few percent of the physically active doping atoms really contribute to the active doping of the semiconductor. Since the solubility limits of the dopants prevent exceeding unlimited concentrations, some 10 19 cm -3 for the Mg for example, the effective dopings are therefore close to 10 17 cm -3 leading to very high layer resistances (about 100 of kQ per square for thicknesses of 50 nm). These values are incompatible with a microwave operation since they would have to be much lower than the typical kΩ.
Actuellement pour les fréquences supérieures à 100GHz, les composants état solide sont essentiellement en InP ou Si(Ge) qui permettent des fonctionnements jusque vers 350GHz en laboratoire mais pour de très faibles puissances émises. Des solutions à base de diodes existent
également mais sont d'un réglage difficile et historiquement difficilement intégrables. Currently for frequencies above 100GHz, the solid state components are essentially InP or Si (Ge) that allow operation up to 350GHz in the laboratory but for very low powers emitted. Solutions based on diodes exist but are difficult to adjust and historically difficult to integrate.
Dans ce contexte, le Demandeur propose un nouveau transistor de puissance à base de matériaux lll-V, à structure verticale (effet de surface faible), unipolaire (pour que des électrons participent à la conduction électrique), comprenant un émetteur, une base et un collecteur, dans lequel la base est métallique. La base métallique est insérée au sein d'alliages de matériaux lll-V, tels que des alliages de GaN. In this context, the Applicant proposes a new power transistor based on materials III-V, with a vertical structure (weak surface effect), unipolar (for electrons to participate in electrical conduction), comprising a transmitter, a base and a collector, in which the base is metallic. The metal base is inserted into alloys of III-V materials, such as GaN alloys.
Plus précisément la présente invention a pour objet un transistor comportant une structure verticale comprenant un émetteur, une base, un collecteur caractérisé en ce qu'il comprend : More precisely, the subject of the present invention is a transistor comprising a vertical structure comprising an emitter, a base, a collector characterized in that it comprises:
- un substrat ; a substrate;
- un sous-collecteur comportant au moins une couche en un premier matériau semiconducteur comprenant au moins un élément III et un élément V dopé n avec un premier taux de dopage ; a sub-collector comprising at least one layer made of a first semiconductor material comprising at least one element III and an n-doped element V with a first doping level;
- un collecteur comportant au moins une couche en un deuxième matériau semiconducteur comprenant au moins un élément III et un élément V dopée n avec au moins un second taux de dopage, ledit au moins second taux de dopage étant inférieur audit premier taux de dopage ; a collector comprising at least one layer made of a second semiconductor material comprising at least one element III and an n-doped element V with at least one second doping level, said at least one second doping level being lower than said first doping level;
- un émetteur comportant au moins une couche en un troisième matériau semiconducteur comprenant au moins un élément III et un élément V dopé n ; an emitter comprising at least one layer made of a third semiconductor material comprising at least one element III and an n-doped element V;
- une couche de base métallique continue, située entre le collecteur et l'émetteur et présentant une épaisseur plus fine que le parcours balistique moyen des électrons dans ce métal, ladite couche de base métallique formant la base du transistor et comprenant un matériau métallique comportant au moins l'élément N ; a continuous metal base layer situated between the collector and the emitter and having a thinner thickness than the average ballistic path of the electrons in this metal, said metal base layer forming the base of the transistor and comprising a metallic material comprising minus the element N;
- la barrière de potentiel (ΦΒΕ) à l'interface matériau métallique /troisième matériau semiconducteur de l'émetteur est supérieure à la barrière de potentiel (ΦΒΟ) à l'interface matériau métallique/ deuxième matériau semiconducteur du collecteur.
Selon des variantes de l'invention, le premier et/ou le deuxième et/ou le troisième matériau semiconducteur est(sont) un alliage de ln -x- yAlxGayN. the potential barrier (Φ Β Ε) at the metallic material / third semiconductor material interface of the emitter is greater than the potential barrier (ΦΒΟ) at the metallic material / semiconductor second material interface of the collector. According to variants of the invention, the first and / or the second and / or the third semiconductor material is (are) an alloy of ln- x- y Al x Ga y N.
Selon des variantes de l'invention, le collecteur comporte au moins une couche en un deuxième matériau semiconducteur lll-V Ιη-ι-χ·. yAlx'Gay'N dopé n avec au moins un second taux de dopage, ledit au moins second taux de dopage étant inférieur audit premier taux de dopage et dans lequel l'émetteur comporte au moins une couche en un troisième matériau semiconducteur lll-V ln -x-yAlxGayN dopé n. According to variants of the invention, the collector comprises at least one layer made of a second semiconductor material III-V Ιη-ι -χ ·. yAlx'Gay'N doped n with at least one second doping level, said at least one second doping level being lower than said first doping level and wherein the emitter comprises at least one layer made of a third semiconductor material III-V ln -xy AlxGa y N doped n.
Selon des variantes de l'invention, le premier et/ou le deuxième et/ou le troisième matériau semiconducteur est(sont) choisi(s) parmi ScAIN ou ScGaN. According to variants of the invention, the first and / or the second and / or the third semiconductor material is (are) chosen from ScAIN or ScGaN.
Selon des variantes, le collecteur peut comprendre différents taux de dopage, voire au sein d'une couche. According to variants, the collector may comprise different doping levels, or even within a layer.
Un des avantages des transistors à base métallique est qu'ils peuvent présenter des fréquences de coupure dépassant le THz avec des tensions de fonctionnement élevées (dépassant la dizaine de volts pour de telles fréquences de coupure). One of the advantages of metal-based transistors is that they can have cutoff frequencies exceeding the THz with high operating voltages (exceeding ten volts for such cutoff frequencies).
Selon des variantes de l'invention, le premier matériau semiconducteur du sous-collecteur est en GaN, le deuxième matériau semiconducteur du collecteur est en GaN, le troisième matériau semiconducteur de l'émetteur est en
ou en ln0,i7AI0,83 ou en
According to variants of the invention, the first semiconductor material of the sub-collector is GaN, the second semiconductor material of the collector is GaN, the third semiconductor material of the emitter is in or in ln 0, i 7 AI 0.83 or in
D'autres alliages sont possibles avec la contrainte que la bande interdite de l'émetteur soit supérieure à celle de la base. La bande de conduction du collecteur doit assurer l'absence de discontinuité défavorable avec celle de la base (alignement de type 2, c'est-à-dire éviter qu'une barrière de potentiel soit à franchir par les électrons injectés entre la base et le collecteur) entraînant des pertes à la collection. Other alloys are possible with the constraint that the bandgap of the transmitter is greater than that of the base. The conduction band of the collector must ensure the absence of discontinuity unfavorable with that of the base (type 2 alignment, that is to say to avoid that a potential barrier is to be crossed by the electrons injected between the base and the collector) resulting in losses to the collection.
Selon des variantes de l'invention, le sous-collecteur et/ou le collecteur et/ou l'émetteur comprend(ennent) une structure multicouche ou une structure graduelle, permettant des résistances d'accès ou de collection plus favorables.
La couche de base peut comprendre avantageusement un métal présentant une maille cristalline compatible avec les alliages du nitrure de gallium choisi parmi et non exclusivement : Nb2N, CrN, MoN, TaN. According to variants of the invention, the sub-collector and / or the collector and / or the emitter comprises (ennent) a multilayer structure or a gradual structure, allowing more favorable access or collection resistances. The base layer may advantageously comprise a metal having a crystalline mesh compatible with the alloys of gallium nitride chosen from and not exclusively: Nb 2 N, CrN, MoN, TaN.
En effet, la base métallique du transistor de l'invention, est ainsi insérée au sein d'alliages de matériaux lll-V, ce qui nécessite que le composé métallique choisi soit compatible des températures d'épitaxie desdits matériaux lll-V et offre une structure cristalline compatible. Les composés métalliques à base d'alliage de nitrure offrent à ce titre une très bonne compatibilité. Indeed, the metal base of the transistor of the invention is thus inserted into alloys of materials III-V, which requires that the selected metal compound be compatible with the epitaxial temperatures of said III-V materials and offers a compatible crystalline structure. The metal compounds based on nitride alloy offer for this reason a very good compatibility.
Selon des variantes de l'invention, la couche métallique comporte une épaisseur inférieure ou égale à 30 nanomètres et préférentiellement inférieure ou égale à 10 nanomètres. According to variants of the invention, the metal layer has a thickness less than or equal to 30 nanometers and preferably less than or equal to 10 nanometers.
Selon des variantes de l'invention, le transistor comprend au moins un contact de reprise de base à la surface de la couche métallique et au moins un contact de reprise de collecteur à la surface du sous-collecteur. According to variants of the invention, the transistor comprises at least one base recovery contact on the surface of the metal layer and at least one collector resumption contact on the surface of the sub-collector.
Selon des variantes de l'invention, au moins le contact de reprise de base à la surface de la couche métallique et au moins le contact de reprise de collecteur à la surface du sous-collecteur comprennent une couche de Ti et/ou une couche d'AI et/ou une couche de Ni et /ou une couche d'Au. According to variants of the invention, at least the base-return contact on the surface of the metal layer and at least the collector-return contact on the surface of the sub-collector comprise a Ti layer and / or a substrate layer. AI and / or a Ni layer and / or an Au layer.
Selon des variantes de l'invention, le substrat est du SiC ou du GaN ou du Si. According to variants of the invention, the substrate is SiC or GaN or Si.
Selon des variantes de l'invention, le premier taux de dopage de type n du premier matériau semiconducteur appartenant au sous-collecteur est supérieur ou égal à 1018 cm"3. According to variants of the invention, the first n-type doping rate of the first semiconductor material belonging to the sub-collector is greater than or equal to 10 18 cm -3 .
Selon des variantes de l'invention, le second taux de dopage du second matériau semiconducteur appartenant au collecteur est de l'ordre de 1017 cm"3, permettant de reculer l'apparition de l'effet Kirk. L'effet Kirk est un effet parasite du transistor qui consiste en l'élargissement de la zone de base au détriment de la zone collecteur à la suite d'une forte densité de porteur majoritaire injectée de la base vers le collecteur. Cet effet est rencontré dans le mode de fonctionnement normal du transistor, au niveau de la jonction base collecteur polarisée en inverse. A un seuil d'injection de porteurs supérieur au dopage de la zone collecteur, il est observé un effacement progressif de la zone de charge d'espace entre base et collecteur. Cet
élargissement de la zone de base conduit ainsi à une diminution du gain hyperfréquence du transistor. According to variants of the invention, the second doping rate of the second semiconductor material belonging to the collector is of the order of 10 17 cm -3 , making it possible to reverse the appearance of the Kirk effect. parasitic effect of the transistor which consists in widening of the base area to the detriment of the collector area as a result of a high density of majority carrier injected from the base to the collector This effect is encountered in the normal operating mode of the transistor, at the collector base junction in reverse polarization, at a carrier injection threshold greater than the doping of the collector zone, a gradual erasure of the space charge area between the base and the collector is observed. widening of the base area thus leads to a decrease in the microwave gain of the transistor.
L'invention sera mieux comprise et d'autres avantages apparaîtront à la lecture de la description qui va suivre donnée à titre non limitatif et grâce aux figures annexées parmi lesquelles : The invention will be better understood and other advantages will become apparent on reading the description which follows given by way of non-limiting example and by virtue of the appended figures among which:
- la figure 1 illustre le diagramme des bandes de conduction d'un transistor à base métallique Si/CoSi2/Si de l'art connu ; FIG. 1 illustrates the conduction band diagram of a Si / CoSi 2 / Si metal-base transistor of the prior art;
- la figure 2 illustre le schéma de principe des bandes de conduction dans un transistor à base métallique à base de FIG. 2 illustrates the block diagram of the conduction bands in a metal-based transistor based on
Ιη-ι-x-yAlxGayN selon l'invention ; Ιη-ι-x- y AlxGa y N according to the invention;
- la figure 3 illustre l'évolution de la hauteur de barrière Schottky du Nickel déposé sur des alliages AlxGa-i-xN décrit dans la littérature ; FIG. 3 illustrates the evolution of the Schottky barrier height of nickel deposited on Al x Ga-i- x N alloys described in the literature;
- la figure 4 illustre une vue en coupe d'un transistor à base métallique selon l'invention. - Figure 4 illustrates a sectional view of a metal-based transistor according to the invention.
Le transistor de la présente invention tire ainsi avantage des champs de claquage élevés d'alliages de matériaux lll-V tels que des alliages de ln -x-yAlxGayN et évite les effets de surface difficiles à maîtriser. Il n'utilise que des porteurs majoritaires évitant les effets de dégradation catastrophiques propres aux composants ambipolaires (TBH pour Transistor Bipolaire à Hétérojonction ou HBT pour « Heterojunction Bipolar Transistor », Laser) et s'affranchit du dopage p qui présente une mauvaise conductivité électrique, tout particulièrement dans les matériaux de grande bande interdite du fait de la mobilité intrinsèque des trous et des effets de passivation des dopants liés à l'hydrogène. The transistor of the present invention takes advantage and high breakdown fields alloys of III-V materials such as ln xy AlxGa alloys are N and avoids surface effects difficult to control. It only uses majority carriers avoiding the catastrophic degradation effects specific to ambipolar components (TBH for Bipolar Strand to Heterojunction or HBT for "Heterojunction Bipolar Transistor", Laser) and is free from p-doping which has poor electrical conductivity, especially in high bandgap materials because of the intrinsic motility of the holes and the passivation effects of the hydrogen-bound dopants.
La base métallique évite également les prises de contact ohmique difficiles en utilisant des jonctions simples métal-métal qui présentent des résistances de contact négligeables (μΩ.ηιηι au lieu de valeurs comprises entre 0,1 Ω. mm et 1 Q.mm). Dans les composants verticaux, la vitesse du composant est essentiellement fixée par l'épaisseur des couches épitaxiales et non par la dimension latérale de motifs tels que la grille dans un transistor à effet de champ. Cela permet d'atteindre des fréquences de coupure des gains hyperfréquences au-delà de 100GHz en utilisant des motifs de tailles
supérieures à 500 nm permettant le recours à des steppers optiques l-line voire G-line et non à des masqueurs électroniques. Les steppers ont l'avantage de permettre des temps d'exposition largement plus courts que ceux des masqueurs électroniques, l'écart étant entre des minutes et des heures. The metal base also avoids difficult ohmic contacting by using simple metal-metal junctions which have negligible contact resistances (μΩ.ηιηι instead of values between 0.1 Ω.mm and 1 Q.mm). In vertical components, the speed of the component is essentially fixed by the thickness of the epitaxial layers and not by the lateral dimension of patterns such as the gate in a field effect transistor. This makes it possible to reach microwave gain cut-off frequencies above 100 GHz by using size patterns greater than 500 nm allowing the use of optical l-line or even G-line optical steppers and not electronic masks. Steppers have the advantage of allowing much shorter exposure times than electronic masks, the difference being between minutes and hours.
La solution de la présente invention permet d'accroître d'un ordre de grandeur les densités de puissance disponible. Même à des fréquences plus faibles, la présente solution est intéressante pour les composants à base de ln -x-yAlxGayN en limitant fortement l'impact des phénomènes de surface (charges) et les pièges en volume. Elle permet l'amélioration du bruit basse fréquence et les effets dispersifs propres aux composants planaires. The solution of the present invention makes it possible to increase by an order of magnitude the available power densities. Even at lower frequencies, the present solution is of interest for the components based on ln -xy AlxGayN by greatly limiting the impact of surface phenomena (charges) and volume traps. It allows the improvement of low frequency noise and dispersive effects specific to planar components.
Les transistors de la présente invention sont dits « Normally-off » (bloqués si pas de tensions appliquées sur la base). Du fait de ce mode de polarisation, l'alimentation des circuits peut ne comporter que des tensions positives, alors que la solution classique HEMT nécessite deux alimentations positive (drain) et négative (grille). Etant verticaux, les composants de la présente invention évitent les effets de surface rencontrés par les composants actuels HEMT. The transistors of the present invention are said to be "Normally-off" (blocked if no voltages applied to the base). Due to this polarization mode, the power supply of the circuits may only include positive voltages, whereas the conventional HEMT solution requires two positive (drain) and negative (gate) power supplies. Being vertical, the components of the present invention avoid the surface effects encountered by current HEMT components.
Les transistors de la présente invention sont des composants unipolaires qui sont moins sensibles aux dégradations catastrophiques subies par les TBH ou les lasers conventionnels qui sont ambipolaires. The transistors of the present invention are unipolar components that are less sensitive to catastrophic damage to conventional TBHs or lasers that are ambipolar.
Leur structure verticale leur confère l'avantage supplémentaire de la compacité. Their vertical structure gives them the added benefit of compactness.
De plus, la couche métallique simplifie la prise des contacts ohmiques sur la couche de base. Les résistances série au niveau de la commande de base (ou de grille) constituent un point très sensible pour la montée en fréquence des composants. In addition, the metal layer simplifies the setting of the ohmic contacts on the base layer. The series resistances at the basic (or gate) control are a very sensitive point for the frequency rise of the components.
L'invention propose d'utiliser les alliages de matériaux lll-V tels que des alliages de ln -x-yAlxGayN pour réaliser des transistors à base métallique. Ces composants connus depuis les années soixante, avaient été tentés de façon non monolithique et décrits dans l'article de Kahng, D. & Atalla, M. M. IEEE-AIEE Solid-State Device Res. Conf. (Carnegie Inst. of Tech., 1960)
Une première réalisation monolithique en silicium : Sylvain Delage, « Etude et la réalisation de transistors à base métallique Si/CoSi2/Si obtenue par épitaxie par jets moléculaires », Thèse (1985), a été réalisée en 1985 et décrite dans l'article de E. Rosencher, S. Delage, Y. Campidelli, F. Arnaud d'Avitaya, "Transistor effect in monolithic Si/CoSi2/Si epitaxial structures", Electronics Letters, Vol. 19, (1984), p.762-764. The invention proposes to use the alloys of III-V materials such as ln xy AlxGayN alloys for making transistors metal base. These known components since the sixties, had been tried in a non-monolithic way and described in the article by Kahng, D. & Atalla, MM IEEE-AIEE Solid-State Device Res. Conf. (Carnegie Institute of Tech., 1960) A first monolithic realization in silicon: Sylvain Delage, "Study and the realization of Si / CoSi 2 / Si-based transistors obtained by molecular beam epitaxy", Thesis (1985), was carried out in 1985 and described in the article E. Rosencher, S. Delage, Y. Campidelli, F. Arnaud of Avitaya, "Transistor effect in monolithic Si / CoSi 2 / Si epitaxial structures", Electronics Letters, Vol. 19, (1984), p.762-764.
Un des points faibles de la démonstration de 1985 provient de l'égalité des hauteurs de barrière de chaque côté de la couche métallique, comme illustré en figure 1 qui montre le diagramme des bandes de conduction d'un transistor à base métallique Si/CoSi2/Si. One of the weak points of the 1985 demonstration comes from the equality of the barrier heights on each side of the metal layer, as illustrated in Figure 1 which shows the conduction band diagram of a Si / CoSi 2 metal-based transistor. /Yes.
La collection des porteurs est dans ce cas très difficile car les électrons injectés dans la base ont un parcours balistique comme attendu, mais ils doivent ensuite franchir une barrière de potentiel identique à celle de l'injection empêchant leur collection. Une collection est cependant possible grâce à un phénomène de force image. En effet les porteurs arrivant près de l'interface métal-semiconducteur voient en regard de l'interface des charges de signe opposé à une distance équivalente. Ce phénomène crée un champ électrique perpendiculaire à la surface abaissant la hauteur de barrière base- collecteur de quelques meV. The collection of carriers is in this case very difficult because the electrons injected into the base have a ballistic course as expected, but they must then cross a barrier of potential identical to that of the injection preventing their collection. A collection is however possible thanks to a phenomenon of force image. In fact, the carriers arriving near the metal-semiconductor interface see opposite the interface of the charges of opposite sign at an equivalent distance. This phenomenon creates an electric field perpendicular to the surface lowering the base-collector barrier height by a few meV.
Selon la présente invention, les alliages utilisés de matériaux lll-V tels que GaN permettent de réaliser des barrières Schottky dissymétriques assurant l'émission et la collection des porteurs. According to the present invention, the alloys used of III-V materials such as GaN make it possible to produce asymmetric Schottky barriers ensuring the emission and collection of carriers.
D'autre part, en utilisant des alliages de matériaux lll-V, il est possible de trouver des métaux présentant une bonne morphologie même pour de faible épaisseur, compatibles de tels matériaux lll-V. On peut par exemple faire référence à des films de Nb2N, notamment décrits dans l'article de David Meyer, Naval Research Laboratory, « Epitaxial Conductors: Transition Métal Nitride Development at NRL », WOCSEMMAD 2016, Tucson, AZ, USA et qui présentent une bonne morphologie même pour des épaisseurs faibles. On the other hand, using alloys of materials III-V, it is possible to find metals having a good morphology even for thin, compatible such materials III-V. For example, reference can be made to films of Nb 2 N, in particular described in the article by David Meyer, Naval Research Laboratory, "Epitaxial Conductors: Metal Transition Nitride Development at NRL", WOCSEMMAD 2016, Tucson, AZ, USA and have a good morphology even for low thicknesses.
Ces films métalliques présentent des résistances de couches de l'ordre de 4 ohms par carré pour une épaisseur de 10Onm. These metal films have layer resistances of the order of 4 ohms per square for a thickness of 10 nm.
Des calculs préliminaires montrent que des composants de 7μηιχ0,5μηι avec une base de Nb2N de 10nm présentent une fréquence de coupure du gain de courant ft d'environ 0,63THz et une fréquence de
coupure du gain en puissance de 0,75THz tout en ayant une tension de claquage de l'ordre de 30V. Preliminary calculations show that components of 7μηιχ0,5μηι with a base of Nb 2 N of 10nm have a cut-off frequency of the current gain ft of approximately 0.63THz and a frequency of cutting power gain of 0.75 THz while having a breakdown voltage of the order of 30V.
Il serait possible d'obtenir des densités de courant de 3x105 Acm"2 avec des densités de puissance atteignant 6 mW μηπ"2. Les fréquences de coupure pourraient atteindre le double de celles des TBH en InP ou SiGe, et la densité de puissance serait d'un ordre de grandeur plus importante. It would be possible to obtain current densities of 3 × 10 5 Acm -2 with power densities up to 6 mW μηπ- 2 . Cutoff frequencies could be twice that of InP or SiGe TBHs, and the power density would be an order of magnitude larger.
La figure 2 illustre à titre d'exemple, un schéma de bande d'un dispositif selon l'invention, comportant un émetteur en ln0,-i7AI0,83GaN, une base en Nb2N et un collecteur en GaN, mettant en évidence que la barrière de potentiel ΦΒΕ à l'interface métal/troisième matériau semiconducteur (correspondant à la barrière base/émetteur) est supérieure à la barrière de potentiel ΦΒο à l'interface métal/ deuxième matériau semiconducteur collecteur (correspondant à la barrière base/collecteur). Les flèches schématisent le parcours des électrons injectés depuis l'émetteur vers le collecteur. FIG. 2 illustrates, by way of example, a band diagram of a device according to the invention, comprising an emitter in ln 0, -i 7 AI 0.83 GaN, a base in Nb 2 N and a collector in GaN , highlighting that the potential barrier Φ Β Ε at the metal / third semiconductor interface (corresponding to the base / emitter barrier) is greater than the potential barrier Φ Β ο at the metal / second semiconductor semiconductor interface (corresponding to the base / collector barrier). The arrows schematize the path of the electrons injected from the transmitter to the collector.
De manière générale, le premier et/ou le deuxième et/ou le troisième matériau semiconducteur est(sont) un alliage de ln -x-yAlxGayN. Generally, the first and / or second and / or third semiconductor material is (are) an alloy of In xy AlxGayN.
L'utilisation de tels alliages de compositions différentes permet l'obtention de hauteurs de barrière métal-semiconducteur différentes. The use of such alloys of different compositions makes it possible to obtain different metal-semiconductor barrier heights.
La figure 3 montre à titre d'exemple l'évolution de la hauteur de barrière Schottky avec des alliages AlxGa-i-xN en fonction de la concentration d'aluminium pour un contact métal Ni comme décrit dans l'article : "Dependence of Ni/AIGaN Schottky barrier height on Al mole fraction", D. Qiao, L. S. Yu, S. S. Lau, J. M. Redwing, J. Y. Lin, and H. X. Jiang, Journal of Applied Physics 87, 801 (2000); doi: 10.1063/1 .371944. FIG. 3 shows, by way of example, the evolution of the Schottky barrier height with Al x Ga-i- x N alloys as a function of the concentration of aluminum for a Ni metal contact as described in the article: " Dependence of Ni / AIGaN Schottky barrier height on Al mole fraction ", Qiao Q, LS Yu, Lau SS, Redwing JM, JY Lin, and Jiang HX, Journal of Applied Physics 87, 801 (2000); doi: 10.1063 / 1 .371944.
Il apparaît ainsi qu'en utilisant deux alliages AlxGa-i-xN de composition différente il est possible d'obtenir deux hauteurs de barrière différentes. En l'occurrence la couche émetteur doit comporter une concentration d'aluminium supérieure à celle de la couche collecteur. Concernant le choix des métaux les mieux adaptés à la structure de transistor à base métallique de l'invention, si l'utilisation de matériaux lll-V tels que les alliages GaN permet une ingénierie des bandes d'énergie et une collection nettement plus aisée que pour les composants silicium, il est nécessaire d'obtenir des métaux compatibles des températures de croissance du GaN et ayant la bonne cristallinité permettant plus
précisément d'obtenir une hétérostructure pouvant être : I n -χ-yAI XG ay N/M étal/ 1 n 1.x- y Al x- Gay N . It thus appears that by using two Al x Ga-i- x N alloys of different composition it is possible to obtain two different barrier heights. In this case the emitter layer must have an aluminum concentration higher than that of the collector layer. Regarding the choice of metals best suited to the metal-based transistor structure of the invention, if the use of III-V materials such as GaN alloys allows energy band engineering and collection much easier than for silicon components, it is necessary to obtain compatible metals GaN growth temperatures and having the good crystallinity allowing more precisely to obtain a heterostructure may be: I n -χ X-YAI G y N / M cal / 1 1. No x - y Al x - N Gay.
Il a précédemment été mentionné le composé métallique Nb2N. En effet des alliages Nb2N (par exemple B-Nb2N) offrent ce type de propriétés physiques avec un accord de maille de 1 % avec le SiC et donc une compatibilité avec la maille cristalline du GaN également. De plus l'élément Nb offre une température de fusion élevée de 2477°C. Des couches épaisses de Nb2N de 100nm d'épaisseur présentent actuellement une résistance de couche de 3,9 ohms par carré. Des hauteurs de barrière de 3,45eV très élevées ont été mesurées avec ΓΑΙΝ. D'autres matériaux sont également des candidats possibles tels que : ScGaN, ScAIN, CrN, MoN, TaN. It has previously been mentioned the metal compound Nb 2 N. In fact alloys Nb 2 N (for example B-Nb 2 N) offer this type of physical properties with a mesh of 1% with SiC and therefore a compatibility with the crystalline mesh of GaN also. In addition, the Nb element has a high melting point of 2477 ° C. Thick Nb 2 N layers of 100 nm thickness currently have a layer resistance of 3.9 ohms per square. Very high 3.45eV barrier heights were measured with ΓΑΙΝ. Other materials are also possible candidates such as: ScGaN, ScAIN, CrN, MoN, TaN.
Les électrons injectés dans la base la franchissent de façon balistique. Seuls les électrons qui ne subissent pas de collision peuvent être collectés. Le libre parcours balistique moyen dans un métal a été étudié pour certains métaux. Pour le CoSi2, il atteint 9nm, pour Ag 27nm, pour Au 22nm, pour Pd 9nm et pour Al 10nm. The electrons injected into the base pass through it in a ballistic manner. Only electrons that do not experience a collision can be collected. The free ballistic range in a metal has been studied for some metals. For CoSi 2 , it reaches 9nm, for Ag 27nm, for Au 22nm, for Pd 9nm and for Al 10nm.
Ces libres parcours moyens sont faibles. Au cas où il serait de 10nm ce qui semble un pire cas, il conviendrait d'utiliser des épaisseurs de l'ordre de 5nm pour obtenir des gains en courant suffisants. Pour des bases aussi fines, il serait toujours possible d'obtenir des fréquences de coupure du gain en courant petit signal ft de 0,6 THz, des fréquences de coupure du gain en puissance petit signal : fmax de 1 THz pour des couches métalliques de 80 ohms par carré (valeur basée sur celle du Nb2N) et des composants comportant des doigts d'émetteur de 0,5μηι.7μηι. These free average courses are weak. In case it is 10nm which seems a worst case, it should be used thicknesses of the order of 5nm to obtain sufficient current gains. For such thin bases, it would still be possible to obtain low signal current gain cutoff frequencies ft 0.6 THz, signal power cut-off frequencies: fmax of 1 THz for metal layers of 80 ohms per square (value based on that of Nb 2 N) and components with transmitter fingers of 0.5μηι.7μηι.
Il est à noter que dans la présente invention, les règles de construction des composants sont similaires à celles des composants TBH à ceci près que le contact ohmique de base métallique est un contact métal/métal. It should be noted that in the present invention, the construction rules of the components are similar to those of the TBH components except that the ohmic metal base contact is a metal / metal contact.
La figure 4 montre le schéma d'une vue en coupe d'un exemple de transistor selon l'invention : FIG. 4 shows the diagram of a sectional view of an example of a transistor according to the invention:
Le transistor à base métallique de l'invention comprend : - un substrat 100 ; The metal-based transistor of the invention comprises: a substrate 100;
- un sous-collecteur 200 ;
- un collecteur 300 ; a sub-collector 200; a collector 300;
- une couche métallique 400 ; a metal layer 400;
- un émetteur 500 ; a transmitter 500;
- au moins un contact de collecteur 310 ; at least one collector contact 310;
- deux contacts de base 410 ; two basic contacts 410;
- un contact d'émetteur 510. an emitter contact 510.
Si la solution la plus classique de transistor consiste à utiliser des composants en forme de ruban, des composants d'autres formes telles que circulaire sont possibles. La combinaison d'éléments individuels est bien évidemment possible comme connue de l'homme de l'art. If the most conventional transistor solution is to use ribbon-shaped components, components of other shapes such as circular are possible. The combination of individual elements is of course possible as known to those skilled in the art.
Par ailleurs, la structure de transistor de la présente invention demeure compatible des solutions de management thermique décrites notamment dans la demande de brevet EP 1276149 (Thomson-CSF, "Composant semiconducteur avec dissipateur thermique intégré", S. Delage, S. Cassette, H. Blanck, E. Chartier, (1995), 95 08994, ou la demande de brevet français publiée 2 737 342, permettant d'envisager des applications en bande S ou X. Le Demandeur a effectué des calculs analytiques pour évaluer les performances électriques d'un transistor à base métallique comparé à celles d'un transistor bipolaire à hétérojonction de l'état de l'art et fournies dans l'article de Zach Griffith, YoungMin Kim, Mattias Dahlstrôm, Arthur C. Gossard, and Mark J. W. Rodwell, « InGaAs-lnP Metamorphic DHBTs Grown on GaAs With Lattice-Matched Device Performance and ft, fmax > 268 GHz », IEEE ELECTRON DEVICE LETTERS, VOL. 25, NO. 10, OCTOBER 2004. Furthermore, the transistor structure of the present invention remains compatible thermal management solutions described in particular in the patent application EP 1276149 (Thomson-CSF, "semiconductor component with integrated heat sink", S. Delage, S. Cassette, H Blanck, E. Chartier, (1995), 95 08994, or the published French patent application 2,737,342, making it possible to envisage applications in the S or X band. The Applicant has carried out analytical calculations to evaluate the electrical performance of a metal-based transistor compared to those of a state-of-the-art heterojunction bipolar transistor and provided in the article by Zach Griffith, Kim YoungMin, Mattias Dahlstrom, Arthur C. Gossard, and Mark JW Rodwell, "InGaAs-lnP Metamorphic DHBTs Grown on GaAs with Lattice-Matched Performance Device and ft, fmax> 268 GHz," IEEE ELECTRON DEVICE LETTERS, VOL 25, NO.10, OCTOBER 2004.
Transistor à base Transistor bipolaire métallique à hétérojonction Transistor-based Bipolar metal transistor with heterojunction
Gain en courant 7 35 Current gain 7 35
Temps de transit 2,08. 10"13 s 3,07. 10"13 s Transit time 2.08. 10 "13 s 3.07, 10 " 13 s
ft 6,33.10" Hz 3,52. 101 1 Hz ft 6.33.10 "Hz 3.52 10 1 1 Hz
fmax 7,55. 10 1 1 Hz 3,1 1 . 10 1 1 Hz fmax 7.55. 10 1 1 Hz 3.1 1. 10 1 1 Hz
Champ de claquage 4 MV/cm 0,5 MV/cm
Tension de claquage 3,27. 101 V 9,81 V Field of breakdown 4 MV / cm 0,5 MV / cm Breakdown voltage 3.27. 10 1 V 9.81 V
Effet Kirk -Je critique 3,2 10 5 A/cm2 1 ,12 10.5 A / cm2 Kirk Effect -I Critical 3.2 10 5 A / cm 2 1, 12 10. 5 A / cm 2
Puissance max 4,57 10"2 W 2,4 10 " 3 W Max power 4,57 10 "2 W 2,4 10 " 3 W
Densité de puissance 13,1 mW /um2 6,86 10 "1 mW /um2 Power density 13.1 mW / μm 2 6.86 10 "1 mW / μm 2
Tableau 1 Table 1
Le transistor à base métallique présente des dimensions de 0,5μηι x 7μηι GaN identiques à celles du transistor THB InP, avec une base métallique en Nb2N de 3,5nm d'épaisseur et le libre parcours balistique moyen est fixé à 20nm. The metal-based transistor has dimensions of 0.5μηι x 7μηι GaN identical to those of the THB InP transistor, with a metal base of Nb 2 N 3.5nm thick and the average free ballistic path is set at 20nm.
Le Tableau 1 montre les valeurs des paramètres clé des transistors. Les paramètres ont été estimés en tablant sur des valeurs physiques disponibles dans la littérature scientifique et met en évidence l'amélioration des performances électriques attendues avec le transistor à base métallique de l'invention. Il est important de mentionner que des fréquences de coupure du gain en puissance supérieures à 1 THz seraient accessibles en augmentant à 6 nm l'épaisseur de la base métallique tous les autres paramètres étant inchangés. Le libre parcours balistique moyen des électrons injectés dans la base métallique gouverne le gain en courant du composant et dans l'exemple donné le gain en courant chuterait à 3. Table 1 shows the values of the key parameters of the transistors. The parameters have been estimated on the basis of physical values available in the scientific literature and highlights the improvement in electrical performance expected with the metal-based transistor of the invention. It is important to mention that power gain cut-off frequencies greater than 1 THz would be accessible by increasing the thickness of the metal base to 6 nm, all other parameters being unchanged. The average free ballistic trajectory of the electrons injected into the metal base governs the current gain of the component and in the example given the gain in current would drop to 3.
Les principaux avantages du transistor de la présente invention sont notamment les suivants et rappelés ci-après : The main advantages of the transistor of the present invention are in particular the following and recalled below:
- moins de sensibilité à la surface (comparé aux HEMT GaN) ; - less surface sensitivity (compared to GaN HEMTs);
- moins d'effets dispersifs liés à la surface et aux pièges en volume d'où un meilleur bruit BF ; - less dispersive effects related to the surface and volume traps resulting in better BF noise;
- une structure verticale permettant d'obtenir des transistors plus compacts ; a vertical structure making it possible to obtain more compact transistors;
- une densité de puissance permettant un facteur 10 par rapport aux composants TBH InP (la meilleure solution actuellement) ; a power density allowing a factor of 10 with respect to the TBH InP components (the best solution at present);
- une possibilité de couvrir un large spectre de fréquences de la RF au THz en jouant sur les bandes d'énergie, les épaisseurs des couches d'émetteur et de collecteur et les niveaux de dopage ;
des contraintes de lithographie relâchées car la vitesse du dispositif est donnée par les épaisseurs de couches déterminées par la croissance épitaxiale ; - a possibility to cover a wide spectrum of frequencies from RF to THz by playing on the energy bands, the thicknesses of the emitter and collector layers and the doping levels; lithography constraints relaxed because the speed of the device is given by the layer thicknesses determined by the epitaxial growth;
une caractéristique « Normally-off » (simplification alimentation électrique) ; a "Normally-off" feature;
un composant unipolaire présentant une meilleure fiabilité (pas de dégradation catastrophique des TBH ou Laser) et permettant d'accepter des densités de défauts cristallins plus élevées à fiabilité égale aux HEMT avec a priori moins de différence entre le claquage base commune et émetteur commun.
a unipolar component exhibiting better reliability (no catastrophic degradation of TBH or Laser) and making it possible to accept higher crystalline defect densities with a reliability equal to the HEMT with a priori less difference between the common base breakdown and the common emitter.
Claims
1 . Transistor comportant une structure verticale comprenant un émetteur, une base, un collecteur caractérisé en ce qu'il comprend : 1. Transistor comprising a vertical structure comprising an emitter, a base, a collector characterized in that it comprises:
- un substrat ; a substrate;
- un sous-collecteur comportant au moins une couche en un premier matériau semiconducteur comprenant au moins un élément III et un élément V dopé n avec un premier taux de dopage ; a sub-collector comprising at least one layer made of a first semiconductor material comprising at least one element III and an n-doped element V with a first doping level;
- un collecteur comportant au moins une couche en un deuxième matériau semiconducteur comprenant au moins un élément III et un élément V dopée n avec au moins un second taux de dopage, ledit au moins second taux de dopage étant inférieur audit premier taux de dopage ; a collector comprising at least one layer made of a second semiconductor material comprising at least one element III and an n-doped element V with at least one second doping level, said at least one second doping level being lower than said first doping level;
- un émetteur comportant au moins une couche en un troisième matériau semiconducteur comprenant au moins un élément III et un élément V dopé n ; an emitter comprising at least one layer made of a third semiconductor material comprising at least one element III and an n-doped element V;
- une couche de base métallique continue, située entre le collecteur et l'émetteur et présentant une épaisseur plus fine que le parcours balistique moyen des électrons dans ce métal, ladite couche de base métallique formant la base du transistor et comprenant un matériau métallique comportant au moins l'élément N ; a continuous metal base layer situated between the collector and the emitter and having a thinner thickness than the average ballistic path of the electrons in this metal, said metal base layer forming the base of the transistor and comprising a metallic material comprising minus the element N;
- la barrière de potentiel (ΦΒΕ) à l'interface matériau métallique/troisième matériau semiconducteur de l'émetteur est supérieure à la barrière de potentiel (ΦΒΟ) à l'interface matériau métallique/ deuxième matériau semiconducteur du collecteur. the potential barrier (Φ Β Ε) at the metallic material / third semiconductor material interface of the emitter is greater than the potential barrier (ΦΒΟ) at the metallic material / semiconductor second material interface of the collector.
2. Transistor selon la revendication 1 , dans lequel le premier et/ou le deuxième et/ou le troisième matériau semiconducteur est(sont) un alliage de ln -x-yAlxGayN. 2. Transistor according to claim 1, wherein the first and / or second and / or third semiconductor material is (are) an alloy of Al xGa y N -xy .
3. Transistor selon la revendication 2, dans lequel le collecteur comporte au moins une couche en un deuxième matériau semiconducteur lll-V In-i-x yAlx Gay N dopé n avec au moins un second taux
de dopage, ledit au moins second taux de dopage étant inférieur audit premier taux de dopage et dans lequel l'émetteur comporte au moins une couche en un troisième matériau semiconducteur lll-V ln -x-yAlxGayN dopé n. 3. Transistor according to claim 2, wherein the collector comprises at least one layer of a second n-doped n-doped doped n-lined material with at least one second level. doping, said at least second doping level being less than said first doping levels and wherein the transmitter comprises at least one layer of a third semiconductor material III-V ln xy AlxGa y N n-doped.
4. Transistor selon la revendication 1 , dans lequel le premier et/ou le deuxième et/ou le troisième matériau semiconducteur est(sont) choisi(s) parmi ScAIN ou ScGaN. The transistor of claim 1, wherein the first and / or second and / or third semiconductor material is (are) selected from ScAIN or ScGaN.
5. Transistor selon la revendication 2, dans lequel le premier matériau semiconducteur du sous-collecteur est en GaN, le deuxième matériau semiconducteur du collecteur est en GaN, le troisième matériau semiconducteur de l'émetteur est en
ou en ln0,i7AI0,83N ou en
5. Transistor according to claim 2, wherein the first semiconductor material of the sub-collector is GaN, the second semiconductor material of the collector is GaN, the third semiconductor material of the transmitter is in or in ln 0, i 7 AI 0.83 N or in
6. Transistor selon l'une des revendications 1 à 5, caractérisé en ce que le sous-collecteur et/ou le collecteur et/ou l'émetteur comprend(ennent) une structure multicouche ou une structure graduelle. 6. Transistor according to one of claims 1 to 5, characterized in that the sub-collector and / or the collector and / or the transmitter comprises (ennent) a multilayer structure or a gradual structure.
7. Transistor à base métallique selon l'une des revendications 1 à 6, dans lequel la couche de base métallique comprend un composé métallique choisi parmi : Nb2N, CrN, MoN, TaN. The metal-based transistor of one of claims 1 to 6, wherein the metal base layer comprises a metal compound selected from: Nb 2 N, CrN, MoN, TaN.
8. Transistor selon l'une des revendications 1 à 7, dans lequel la couche de base métallique comporte une épaisseur inférieure ou égale à 30 nanomètres. 8. Transistor according to one of claims 1 to 7, wherein the metal base layer has a thickness less than or equal to 30 nanometers.
9. Transistor selon la revendication 8, dans lequel la couche de base métallique comporte une épaisseur inférieure ou égale à 10 nanomètres. 9. Transistor according to claim 8, wherein the metal base layer has a thickness less than or equal to 10 nanometers.
10. Transistor selon l'une des revendications 1 à 9, comprenant au moins un contact de reprise de base à la surface de la couche de base métallique et au moins un contact de reprise de collecteur à la surface du sous-collecteur.
10. Transistor according to one of claims 1 to 9, comprising at least one base recovery contact on the surface of the metal base layer and at least one collector recovery contact on the surface of the sub-collector.
1 1 . Transistor selon l'une des revendications 1 à 10, dans lequel le substrat est du SiC ou du GaN ou du Si. 1 1. Transistor according to one of Claims 1 to 10, in which the substrate is SiC or GaN or Si.
12. Transistor selon l'une des revendications 1 à 1 1 , dans lequel le premier taux de dopage est supérieur à 1018 cm"3. 12. Transistor according to one of claims 1 to 1 1, wherein the first doping rate is greater than 10 18 cm -3 .
13. Transistor selon l'une des revendications 1 à 12, dans lequel le second taux de dopage est de l'ordre de 1017 cm"3.
13. Transistor according to one of claims 1 to 12, wherein the second doping rate is of the order of 10 17 cm -3 .
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| EP18742820.6A EP3659181A1 (en) | 2017-07-27 | 2018-07-26 | Metal-based transistor comprising materials comprising at least one group iii element and one group v element |
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| FR1700798A FR3069704B1 (en) | 2017-07-27 | 2017-07-27 | METALLIC TRANSISTOR COMPRISING III-V MATERIALS |
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| WO2014039550A1 (en) * | 2012-09-04 | 2014-03-13 | Carnegie Mellon University | A hot-electron transistor having metal terminals |
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- 2018-07-26 EP EP18742820.6A patent/EP3659181A1/en active Pending
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| EP3659181A1 (en) | 2020-06-03 |
| FR3069704A1 (en) | 2019-02-01 |
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