High electron mobility transistor (HEMT), transistor assembly, method for controlling HEMT, and method for manufacturing HEMT

Abstract

A transistor with high electron mobility (High Electron Mobility Transistor (HEMT)) is described, comprising a first layer and a second layer. The first layer comprises a first material made of a first nitride compound. The first nitride compound comprises a group III element. The second layer comprises a second material made of a second nitride compound. The second nitride compound comprises a group III element. A major surface of the second layer is disposed opposite a major surface of the first layer such that a charge zone is formed along the major surface of the second layer. The HEMT further comprises a gate electrode disposed opposite the second layer, at least in a region, such that the second layer is disposed between the first layer and the gate electrode. Furthermore, the HEMT comprises a third layer disposed between the gate electrode and the second layer. The third layer comprises a ferroelectric third material made of a third nitride compound or a ferroelectric third material made of an oxide compound including zinc.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to High-Electron-Mobility-Transistors (HEMTs). Further embodiments relate to transistor assemblies. Further embodiments relate to methods for controlling HEMTs. Further embodiments relate to methods for manufacturing HEMTs. [Background technology]

[0002] The structure of a HEMT component typically has a two-dimensional electron gas (2DEG) at the interface during the manufacturing process, forming, for example, an AlGaN / GaN structure. Due to the permanent development of a conductive 2DEG at the interface between two III-N-based layers, HEMTs based thereon are permanently in the on-state (normally on structure) without the additional application of a gate voltage. This has drawbacks, firstly, in terms of safety (the component is always on, even if the gate voltage supply fails), and furthermore, makes the manufacturing of integrated logic gates based on this technology more difficult.

[0003] However, for widespread use in power electronics circuits, for example, a normally-off structure is required, in contrast to the normally-on structure described above, in which the 2DEG is either interrupted or conducts only a small cutoff current without an applied gate voltage. Today, this function is pursued by various alternative approaches, such as Schottky gate structures, recessed gate structures, or under-gate fluorine ion implantation. However, all of these variations have very low threshold voltages (Vth), in the range of less than or close to 1 V. Higher threshold voltages can be achieved with p-doped AlGaN gates. However, this solution has the disadvantage of potentially high gate leakage currents, depending on the effectiveness of the gate contact metallization as a Schottky or ohmic contact. When a Schottky contact is formed, the depletion zone resulting from the p-GaN reduces direct control of the 2DEG over the gate potential.

[0004] Alternatively, a III-N heterostructure-based normally-off HEMT can also be achieved through the use of ferroelectric (FE) materials. Similar to the concept of FE field-effect transistors (FE-FETs) for storage applications, a variable voltage offset can be integrated into the gate stack by shifting charges within the ferroelectric material. As a result, the gate voltage can be shifted so that the threshold voltage exceeds 0 V and the transistor is non-conducting, even without applying a gate voltage. This approach has previously been implemented with established oxide-based ferroelectrics, such as LiNbO3, Pb(Zr,Ti)O3, BaTiO3, and HfO2 compounds [Hao12, Zhu18, Li19, Hao17, Yan17, Teo19]. For example, U.S. Patent Application Publication No. 2019 / 0115445 describes the use of ferroelectric materials in the gate stack with a maximum thickness of tcap / 2*α*εcap to achieve a high threshold frequency despite a higher cap layer thickness. CN107316901 describes a FE-HEMT containing HfO2 as the FE gate. CN107369704 describes a FE-HEMT containing a multilayer gate structure with a gate dielectric made of AlN or Al2O3 and a ferroelectric HfZrO layer. CN102299576 uses LiNbO3 or LiTaO3 as an alternative FE material. TW201906163 describes a component including a gate electrode that blocks the 2DEG and contains a ferroelectric material, which can act as a back gate. JP2010-206048 also describes a HEMT with an oxide FE gate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent Application Publication No. 2019 / 0115445 [Patent Document 2] Chinese Patent Application Publication No. 107316901 [Patent Document 3] Chinese Patent Application Publication No. 107369704 [Patent Document 4] Chinese Patent No. 102299576 [Patent Document 5] Taiwan Patent Application Publication No. 201906163 [Patent Document 6] Japanese Patent Application Laid-Open No. 2010-206048 Summary of the Invention

[0006] A HEMT that can stably set the threshold voltage over a wide range is desirable. One embodiment of the present invention provides a HEMT comprising a first layer and a second layer. The first layer includes a first material comprising a first nitride compound. The first nitride compound includes a Group III element. The second layer includes a second material comprising a second nitride compound. The second nitride compound includes a Group III element. A major surface of the second layer is disposed opposite a major surface of the first layer such that a charge zone is formed along the major surface of the second layer. The charge zone may, for example, represent a region around a local extremum of a potential profile perpendicular to the major surface of the first layer. For example, the charge zone may provide a conduction channel in the active state of the HEMT and be depleted in the inactive state of the HEMT. The HEMT further comprises a gate electrode disposed opposite the second layer in at least a region such that the second layer is disposed between the first layer and the gate electrode. The HEMT further comprises a third layer disposed between the gate electrode and the second layer. The third layer includes a ferroelectric third material comprising a third nitride compound or a zinc-containing oxide compound.

[0007] Ferroelectric materials made of nitride compounds or oxide compounds containing zinc can have particularly high polarization. Embodiments of the present invention are based on the finding that these materials are therefore particularly well suited for implementing HEMTs. The arrangement of the third layer relative to the second layer can significantly shift the threshold voltage HEMT due to the high polarization. This allows HEMTs with higher threshold voltages and thus a larger operating range. In particular, positive threshold voltages, even large positive threshold voltages, are possible, which disable the HEMT when no voltage is applied to the gate electrode, and in this state the leakage current is particularly low. Oxide ferroelectrics have a dielectric constant of 1-40 μC / cm. 2 , but for materials used in accordance with the present invention, this value is up to 100 μC / cm 2A larger polarization has the advantage that a larger offset is applied to the gate electrode, and therefore the on-state can be achieved only with a high external current, making the component more closed and safer. The inventors have also found that polarization in ferroelectric nitride or oxide components or oxides is particularly stable. For example, these materials have a high Curie temperature. As a result, the polarization of the third layer is stable even at high operating temperatures. The maximum operating temperature of these materials can exceed 1000°C, thus significantly higher than the maximum operating temperature of oxide ferroelectrics (up to 350°C). Therefore, HEMTs according to the present invention are particularly suitable for power electronics components, such as current converters. High-temperature stability also allows for a high degree of flexibility in the selection of the HEMT manufacturing process, for example, by a gate-first process. Furthermore, it may be possible to manufacture HEMTs by processes in which the gate electrode or the FE third layer is processed from the front side. Furthermore, the ferroelectric material used according to the present invention can be based purely on pyroelectric materials, thus offering excellent polarization stability and, therefore, for example, high long-term stability. This prevents the transistor from unintentionally returning to its initial state after the polarization has been set, thus preventing, for example, a change from a tension state to a conductive state. Ferroelectric nitride compounds or oxide-zinc compounds, in particular, have higher operating temperatures and long-term stability than oxide ferroelectrics, but at the same time, require a relatively low temperature budget for fabrication. In certain embodiments, the third material is a third nitride compound, which has the advantage over HEMTs that include oxide materials of preventing reaction at the oxide interface between the oxide material and the III-N structure, which has a positive effect on the long-term stability of the ferroelectric and the transistor characteristics of the heterostructure.

[0008] In an embodiment, the third material has a wurtzite crystal structure. The selection of a material with a wurtzite crystal structure as the third material allows for particularly convenient fabrication of the third layer in combination with the first layer in the second layer. For example, using a material with a wurtzite structure (e.g., a III-N semiconductor or ZnO) as the third material allows for epitaxial deposition (e.g., stacked one on top of the other) of a layer sequence consisting of the first layer, the second layer, and the ferroelectric third layer, thereby achieving particularly favorable material properties, for example, in terms of defect density, in the ferroelectric part of the gate structure. This allows, for example, a boundary layer between the second layer and the third layer that is particularly low in defects. The possibility of epitaxial deposition of the first, second, and third layers further enables a simple fabrication process.

[0009] In embodiments in which the third material includes a third nitride compound, the third nitride compound includes one or more Group III elements. Group III nitride compounds are often semiconductor materials with large bandgaps, which allows HEMTs to be constructed with particularly low losses. Furthermore, Group III nitride compounds can have high polarization. Because many Group III nitrides have a wurtzite crystal structure, Group III nitrides can combine the advantages of the wurtzite crystal structure with the advantages of a large bandgap and high polarization.

[0010] In an embodiment, the one or more group III elements of the third nitride compound are one or more of Al, Ga, or In. These group III nitride compounds can have a high degree of polarization. For example, the third nitride compound includes Al, Ga, In, AlGa, InGa, or InAl.

[0011] In an embodiment, the third material includes a transition metal. Thus, in an embodiment, the third nitride compound or oxide-zinc compound includes a transition metal. The inventors have found that materials containing transition metals, particularly those with a wurtzite structure, tend to have lower coercivity than corresponding materials that do not include transition metals. In particular, materials containing transition metals may have a coercivity less than the breakdown field strength, thereby making these materials ferroelectric. For example, nitride compounds containing transition metals may be ferroelectric in contrast to their corresponding pure nitride compounds. This is particularly applicable to Group III nitride compounds. Thus, zinc-containing nitride compounds or oxide compounds that may further include a transition metal are a good compromise between high polarization and the presence of ferroelectricity.

[0012] In an embodiment, the transition metal is Sc 、 The third material is Nb, Ti, or Y. Nitride compounds containing these transition metals, particularly Group III nitride compounds containing these transition metals, may be ferroelectric and may have a particularly high degree of polarization and / or a particularly high temperature of use. For example, the third material is AlScN or GaScN. The polarization of AlScN or GaScN is 100 μC / cm 2 and thus may allow a particularly efficient shifting of the threshold voltage. Furthermore, the operating temperatures of AlScN and GaScN can exceed 1000°C.

[0013] In embodiments where the third material is a third nitride compound and the third nitride compound includes one or more Group III elements, the stoichiometric proportion of the transition metal in the third material is 10% to 50% of the total stoichiometric proportion of the one or more Group III elements and the transition metal in the third material. In embodiments where the third material is an oxide compound, the stoichiometric proportion of the transition metal in the third material is 10% to 50% of the total stoichiometric proportion of the zinc and the transition metal in the third material. The inventors have found that such a proportion of transition metal can achieve a second material that is ferroelectric and has a high degree of polarization. Polarization can decrease as the proportion of transition metal increases, and a proportion of less than 50% can ensure a particularly high degree of polarization of the second material. Therefore, it is possible to generate a high charge carrier density in the charge zone along the major surfaces of the first layer and / or second layer. A proportion greater than 10% can ensure that the second material is ferroelectric.

[0014] In an embodiment, the gate electrode and the third layer are part of a gate structure that is positioned opposite the second layer in a region, so that the charge carrier density in the charge zone can be switched or set in a region on the opposite side of the gate structure.

[0015] In some embodiments, the HEMT further includes a fourth layer disposed between the second layer and the third layer. The fourth layer comprises a conductive material. The third layer is thereby disposed between the fourth layer and the gate electrode. Therefore, by establishing a voltage between the fourth layer and the gate electrode, an electric field can be generated, thereby setting the polarization, e.g., the polarization direction and / or polarization degree, of the third material of the third layer, and thus the threshold voltage of the HEMT. Compared to embodiments in which an electric field is applied between the gate electrode and the charge zone, setting the polarization of the third layer without a conductive layer between the second and third layers provides the advantage that the relationship between the electric fields applied to the second and third layers can be set on the surface of the fourth layer, e.g., to prevent electrical breakdown through the second layer. Furthermore, the fourth layer can create more favorable growth conditions for the third layer, e.g., allowing the third layer to be deposited at a lower temperature.

[0016] In an embodiment, the HEMT further comprises an insulating layer disposed between the second layer and the third layer or between the second layer and the fourth layer. The insulating layer comprises an electrically insulating material, for example, Al2O3, GaN, or AlN. The insulating layer can passivate a further major surface of the second layer opposite to the major surface of the second layer.

[0017] In an embodiment, the gate structure includes a fourth layer disposed between the second layer and the third layer, the fourth layer including a fourth conductive material, and the properties and advantages of the fourth layer may correspond to those of the fourth layer described above.

[0018] In an embodiment, the gate structure further comprises an insulating layer disposed between the second layer and the third layer or between the second layer and the fourth layer. The insulating layer comprises an electrically insulating material. The properties and advantages of the insulating layer may correspond to those of the insulating layer described above.

[0019] In an embodiment, the fourth material is one of TiN, NbN, Pt, Al, Ti, Ni, and Mo.

[0020] In an embodiment, the combination of the first material and the second material is one of AlGaN / GaN, AlScN / GaN, AlN / GaN, and AlScN / GaScN.

[0021] In an embodiment, the HEMT includes an intermediate layer disposed between the first layer and the second layer. The intermediate layer includes a material made of a nitride compound. The intermediate layer can change the location of the charge zone, for example, in the first layer or at a major surface of the first layer, so that it is spaced apart from the second layer (the charge zone can also extend into the intermediate layer). The first layer, in an embodiment, can be epitaxially fabricated so that the charge zone can have a particularly high conductivity when at least a majority of it is located within the first layer, and therefore can be particularly free of defects.

[0022] In an embodiment, the material of the intermediate layer is either AlN or GaN. In embodiments, the polarization state of the third material can be set by applying a voltage to the gate electrode. In these embodiments, the threshold voltage of the HEMT, at which the conduction channel through the charge zone changes between an enabled state and an disabled state, depends on the polarization state of the third material. The threshold voltage can refer to, for example, the voltage required between the gate electrode and the charge zone that is intended to change between the enabled state and the disabled state. The change between the enabled state and the disabled state can be characterized, for example, by the conductivity or resistance of the charge zone. Thus, the threshold voltage of the HEMT can be set by applying a voltage to the gate electrode.

[0023] In some embodiments, the third material has a first polarization state. When the third material is in the first polarization state, the threshold voltage of the HEMT is positive. The polarization state can be characterized by a polarization direction and a polarization degree. In some embodiments, where the charge zones are configured to form a 2DEG, the polarization direction of the third material in the first polarization state can point at least partially outward from the charge zones. A positive threshold voltage means that the HEMT is disabled when no voltage is applied to the gate electrode, i.e., when the HEMT is in a normally-off state.

[0024] In some embodiments, the third material further has a second polarization state, and when the third material is in the second polarization state, the threshold voltage is negative. In some embodiments, the polarization degree of the second polarization state can be less than the polarization degree of the first polarization state. In further embodiments, the polarization direction of the second polarization state can at least partially face the charge zone. The negative threshold voltage means that the HEMT is enabled when no voltage is applied to the gate electrode, i.e., when the HEMT is in a normally-on state. Therefore, by setting the polarization state of the third material between the first and second polarization states, the HEMT can be switched between a normally-off state and a normally-on state.

[0025] In an embodiment, a gate electrode is disposed within the gate electrode region, such that a polarization state of a third material in a first region of the third layer opposite the gate electrode region can be set by applying a voltage to the gate electrode. The third layer further includes a second region different from the first region. The third material in the second region of the third layer is in a polarization state such that a charge zone region of the charge zone opposite the second region is in a conductive state.

[0026] In an embodiment, the HEMT includes a source region and a drain region. A charge zone is electrically disposed in series between the source and drain regions. Setting the charge carrier density in the charge zone, for example, by applying a voltage to the gate electrode or by setting the polarization state of a third material, allows for setting the conductivity between the source and drain regions.

[0027] A further embodiment of the present invention provides a transistor assembly including a HEMT according to the present invention, further comprising a control signal generator configured to apply a voltage to the gate electrode to set a polarization direction in a region of the third layer opposite the gate electrode. Setting the polarization direction can effectively set the threshold voltage of the HEMT. For example, the third layer in the region opposite the gate electrode can be fully or substantially fully polarized in one direction by applying a voltage having a magnitude greater than a critical value.

[0028] In an embodiment, the control signal generator is configured to set a polarization degree in a region of the third layer opposite the gate electrode by applying a voltage to the gate electrode to set a threshold voltage of the HEMT. For example, to set the polarization degree, a voltage can be selected that results in a non-uniform polarization of the third material in the region opposite the gate electrode. Setting the polarization degree allows the threshold voltage to be precisely set.

[0029] In an embodiment, the control signal generator is configured to apply a first voltage between the gate electrode and the charge zone to set the threshold voltage to a positive value, and to apply a second voltage between the gate electrode and the charge zone to set the threshold voltage to a negative value.

[0030] A further embodiment of the present invention provides a method of controlling a HEMT according to the present invention, the method comprising applying a voltage to the gate electrode to set a threshold voltage of the HEMT that changes a conduction channel through the charge zone between an active state and an inactive state to set the direction and / or degree of polarization of the third material, thereby allowing the threshold voltage to be set depending on the application of the HEMT.

[0031] A further embodiment of the present invention provides a method of controlling a HEMT according to the present invention, the method comprising applying a first voltage to the gate electrode to set the polarization direction and / or degree of polarization of the third material such that the threshold voltage of the HEMT, which changes the conduction channel through the charge zone between an enabled state and an disabled state, is positive, thereby allowing the HEMT to operate in a normally-off state.

[0032] A further embodiment of the present invention provides a method for fabricating a HEMT. The method includes providing a layer structure including a first layer, a second layer, and a third layer. The third layer includes a ferroelectric material. The layer structure is provided such that the second layer is disposed between the first layer and the third layer. The layer structure is further provided such that a major surface of the second layer is disposed opposite a major surface of the first layer. The layer structure is provided such that a charge zone is formed along the major surface of the first layer. The method further includes applying source and drain contacts such that the charge zone is disposed electrically in series between the source and drain contacts. The method further includes temperature treating or annealing the layer structure together with the source and drain contacts.

[0033] The temperature treatment can achieve or improve ohmic contact between the source contact and the charge zone, or between the drain contact and the charge zone. The inventors have found that HEMTs can be manufactured in a particularly simple manner if the temperature treatment is carried out at a point in the manufacturing process where the layer structure includes a third layer.

[0034] According to one embodiment, providing the layer structure includes epitaxially applying a first layer and a second layer, such that a major surface of the second layer is disposed opposite a major surface of the first layer, a charge zone is formed along a major surface of the first layer, and the first layer includes a first material having a wurtzite crystal structure and the second layer includes a second material having a wurtzite crystal structure. Further, providing the layer structure includes epitaxially applying a ferroelectric third layer, such that the second layer is disposed between the first and third layers, and the third layer includes a ferroelectric third material having a wurtzite crystal structure.

[0035] A further embodiment of the present invention provides a method for fabricating a HEMT. The method includes epitaxially applying a first layer and a second layer such that a major surface of the second layer is disposed opposite a major surface of the first layer and a charge zone is formed along the major surface of the first layer. The epitaxial application of the first layer and the second layer is performed such that the first layer includes a first material having a wurtzite crystal structure and the second layer includes a second material having a wurtzite crystal structure. The method further includes epitaxially applying a ferroelectric third layer such that the second layer is disposed between the first layer and the third layer and the third layer includes a ferroelectric third material having a wurtzite crystal structure.

[0036] The inventors have found that HEMTs can be produced in a particularly simple and defect-free manner in that the first, second and third layers are produced epitaxially. To this end, it is particularly advantageous if the first, second and ferroelectric third layers have a wurtzite crystal structure.

[0037] Embodiments of the invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0038] [Figure 1] 1 is a schematic diagram of a HEMT according to an embodiment. [Figure 2] 1 is a schematic diagram of a further embodiment of a HEMT with a gate electrode. [Figure 3] 1 is a schematic diagram of a further embodiment of a HEMT with a gate structure. [Figure 4] 3 is a schematic diagram of a further embodiment of a HEMT with a gate electrode disposed within the region. [Figure 5] 1 is a schematic diagram of a further embodiment of a HEMT with a gate structure. [Figure 6] FIG. 1 is a flow diagram of a method for switching a HEMT according to one embodiment. [Figure 7] FIG. 10 is a flow diagram of a method for switching a HEMT according to a further embodiment. [Figure 8] FIG. 1 is a flow diagram of a method for manufacturing a HEMT according to an embodiment. [Figure 9] FIG. 10 is a flow diagram of a method for manufacturing a HEMT according to a further embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0039] Hereinafter, the embodiments of the present invention will be described in detail using the accompanying description. In the following description, many details are described to provide a more complete explanation of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that other embodiments can be implemented without these specific details. Features of different described embodiments can be combined with each other unless the features of the corresponding combinations are mutually exclusive or unless such combinations are explicitly excluded.

[0040] It should be noted that identical or similar elements, or elements having the same function, may be given the same or similar reference numerals or the same names, and repeated descriptions of elements given the same or similar reference numerals or the same names are typically omitted. Descriptions of elements having the same or similar reference numerals or the same names are interchangeable.

[0041] FIG. 1 is a schematic diagram of a HEMT 100 according to one embodiment of the present invention. The HEMT 100 includes a first layer 110 and a second layer 120. The first layer 110 includes a first material 111 made of a first nitride compound. The first nitride compound includes a Group III element. The second layer 120 includes a second material 121 made of a second nitride compound. The second nitride compound includes a Group III element. A major surface 122 of the second layer 120 is disposed opposite the major surface 112 of the first layer 110 such that a charge zone 160 is formed along the major surface 112 of the first layer. The HEMT further includes a gate electrode 170. The gate electrode 170 is disposed opposite the second layer 120, at least in a region such that the second layer 120 is disposed between the first layer 110 and the gate electrode 170. The HEMT further includes a third layer 130. The third layer 130 is disposed between the gate electrode 170 and the second layer 120. The third layer 130 includes a ferroelectric third material 131. The third material 131 is made of a third nitride compound. Alternatively, the third material 131 is made of a zinc-containing oxide compound, such as zinc oxide or a zinc oxide compound.

[0042] 1 shows a Cartesian coordinate system chosen as an example. In an embodiment, the first layer 110, the second layer 120, and the third layer 130 may be arranged along the z direction, and each layer may extend in the xy plane.

[0043] In an embodiment, the first layer 110, the second layer 120, the third layer 130, and the gate electrode 170 are part of a layer structure. Each layer of the layer structure may include a major surface and a further major surface opposite the major surface. The major surfaces of the layers may be arranged parallel to each other along a major direction of the layer structure. In an embodiment, the first layer 110, the second layer 120, the third layer 130, and the gate electrode 170 may be arranged parallel to the xy plane.

[0044] A layer structure can be characterized, for example, in that its two layers are separated from each other by at least an interface. Thus, the interface between two layers of a layer structure arranged adjacent to each other can be formed from the opposing main surfaces of the two layers. In this case, the interface can constitute an interface between two different materials that can differ from each other, for example, by their composition and / or their structure.

[0045] The opposed arrangement of the major surfaces of the first layer and the second layer may mean that the major surfaces are disposed opposite each other. As shown in Figure 1, the major surface 112 of the first layer 110 faces the second layer 120, and correspondingly, the major surface 122 of the second layer 120 faces the first layer.

[0046] For example, first material 111 and second material 121 are semiconducting materials whose bandgaps are matched to one another such that an extremum of the potential curve in the z direction that can provide charge zone 160 is formed along major surface 112. The extremum can be a minimum such that a 2DEG can be formed along major surface 112.

[0047] In an embodiment, the combination of the first material 111 and the second material 121 is one of AlGaN / GaN, AlScN / GaN, AlN / GaN, and AlScN / GaScN.

[0048] In an embodiment, both the first material and the second material have a wurtzite crystal structure.

[0049] Since the third material 131 is ferroelectric, the polarization state of the third material 131 can be set by subjecting the third material 131 to an electric field. The polarization state of a ferroelectric material can also be maintained after the application of an electric field, for example, by applying an electric field of sufficient magnitude having an opposite direction. For example, to generate the electric field, a voltage can be applied between the gate electrode 170 and the charge zone 160, for example, via the source or drain region. The third material 131 in the third layer 130 or in a considered region of the third layer 130 can be completely polarized in one direction or partially polarized. For example, individual local domains can be polarized in one direction, while further domains can be unpolarized or polarized in a different direction. The polarization state of the third material 131 or a considered region of the third material 131 can be related to the polarization averaged over the third material 131 or the considered region of the third material 131. In FIG. 1, as an example, a first polarization state 134 in which the polarization direction is at least partially directed away from the second layer 120 and a second polarization state 134′ in which the polarization direction is at least partially directed towards the second layer 120 are shown.

[0050] The polarization of the third material 131 can affect the polarization of the charge zone 160 in a manner similar to the electric field applied by the gate electrode. Depending on the polarization state of the third material 131, the charge zone 160 can be depleted, i.e., blocked, or conductive accordingly. Furthermore, the potential of the charge zone 160 can be varied using the field effect by applying a voltage between the gate electrode 170 and the charge zone 160 to change the charge carrier density in the region of the charge zone 160 opposite the gate electrode 170, thereby enabling or disabling the conductivity of the charge zone 160. The voltage required between the gate electrode 170 and the charge zone 160 to change the conduction channel through the charge zone 160 between an enabled and disabled state may also be referred to as the threshold voltage of the HEMT. In an embodiment, the degree of polarization of the third material 130 can be adjusted to gradually set the threshold voltage of the HEMT.

[0051] Thus, in embodiments where the majority of charge carriers in charge zone 160 are electrons, the charge zone can include or be formed by a 2DEG, and polarization direction of the third material in the z-direction can cause a positive shift in the threshold voltage of the HEMT, e.g., first polarization state 134. Polarization direction of the third material in the z-direction can cause a negative shift in the threshold voltage of the HEMT, e.g., second polarization state 134'. In this case, the magnitude of the threshold voltage shift can depend on the degree of polarization. That is, a transition between a positive and a negative threshold voltage can be achieved in embodiments by changing the degree of polarization of the third layer, without necessarily changing the polarization direction.

[0052] The strength of the electric field that may be required to change or switch the polarization of third material 131 may be, in embodiments, 0.1 MV / cm to 8 MV / cm. The thickness of third layer 130 may be, for example, in the range of 5 to 1000 nm. For example, the strength of the electric field to switch the polarization may be affected by the selection of the thickness of third layer 130.

[0053] In embodiments where the majority of charge carriers in the charge zone are electrons, the HEMT can be configured such that the threshold voltage (taking into account sign) decreases by a factor of at least 1.2, 1.5, 2, or 5, e.g., by more than 50%, or more than 30%, or more than 10%, for voltages at which the polarization of the third material 131 changes substantially. It is therefore possible to ensure that an electric field sufficient to set the polarization of the third material to the second polarization state can be established between the charge zone and the gate electrode.

[0054] In an embodiment, the polarization state of the third material 131 can be set by applying a voltage to the gate electrode 170. The threshold voltage of the HEMT, which changes the conduction channel through the charge zone 160 between an active and inactive state, depends on the polarization state of the third material 131.

[0055] In an embodiment in which the charge zone 160 forms a 2DEG, in the conductive state, a polarization direction of the third material 131 that faces at least partially towards the second layer 120, i.e., away from the z-direction, can result in a shift in the threshold voltage to a positive value, while a polarization direction of the third material 142 that faces at least partially away from the second layer 120, i.e., towards the z-direction, can result in a shift in the threshold voltage to a negative value.

[0056] In an embodiment, the third material 131 has a first polarization state. When the third material 131 is in the first polarization state, the threshold voltage of the HEMT is positive. For example, the first polarization state may be a polarization state in which the polarization direction is oriented at least partially along the z-direction, such as polarization state 134. In an embodiment in which the charge zones 160 form a 2DEG, a positive threshold voltage may mean that in the conductive state, a conduction channel through the charge zones 160 is disabled when no voltage is applied to the gate electrode.

[0057] In an embodiment, the third material 131 also has a second polarization state. When the third material 131 is in the second polarization state, the threshold voltage of the HEMT is negative. For example, the second polarization state may be a polarization state whose polarization direction is oriented at least partially opposite the z-direction, e.g., opposite to the first polarization state, e.g., polarization state 134′. Alternatively, the second polarization state may have the same polarization direction as the first polarization state but a lower polarization degree than the first polarization state. In an embodiment in which the charge zone 160 forms a 2DEG, in the conductive state, a negative threshold voltage may mean that a conduction channel is possible through the charge zone 160 when no voltage is applied to the gate electrode.

[0058] In an embodiment, HEMT 100 further includes source region 172 and drain region 174, arranged such that charge zone 160 is electrically arranged in series between source region 172 and drain region 174. The arrangement of source region 172 and drain region 174 should be understood as just one example. For example, source region 172 and drain region 174 can be arranged adjacent to first layer 110 and / or adjacent to second layer 120. In a conductive state, charge zone 160 can provide a conduction channel between source region 172 and drain region 174. Thus, by applying a voltage to gate electrode 170, the conduction channel between source region 172 and drain region 174 can be enabled or disabled.

[0059] In an embodiment, the third material 131 has a wurtzite crystal structure.

[0060] Thus, in an embodiment, the first material 111, the second material 121, and the third material 131 may have a wurtzite crystal structure.

[0061] In an embodiment, the third material 131 includes a nitride compound containing one or more group III elements, for example, the nitride compound of the third material 131 includes one or more of Al, Ga, and In.

[0062] In both cases where the third material 131 is a nitride compound and where the third material 131 is an oxide compound containing zinc, the third material 131 can include a transition metal. The transition metal can optionally be Sc 、 It may be one of Nb, Ti, or Y. In an embodiment, the third material is AlScN or GaScN.

[0063] In embodiments, the third material 131 is a nitride compound containing one or more Group III elements and a transition metal. In these embodiments, the stoichiometric proportion of the transition metal in the nitride compound of the third material 131 can be between 10% and 50% of the total stoichiometric proportion of the one or more Group III elements and the transition metal in the nitride compound. For example, the third material 131 can be a compound represented by the chemical formula A (1-x) T x N, in which A represents a Group III element or a plurality of different Group III elements, T represents a transition metal, N is nitrogen, and x is 0.1 to 0.5.

[0064] In embodiments, the third material 131 is an oxide compound containing one or more Group III elements and a transition metal. In these embodiments, the stoichiometric proportion of the transition metal in the oxide compound of the third material 131 is: oxidation It can be 10% to 50% of the total stoichiometric proportion of zinc and transition metals in the compound. 。

[0065] In an embodiment, the third material 131 has a lower coercivity than the second material 121. Therefore, the second material 121 may also be ferroelectric. For example, the third material 131 has a lower coercivity than the second material 121 in order to switch or change the polarization of each material in a direction perpendicular to the major surface of the second layer.

[0066] As a result, the polarization direction of the third material can be changed or switched by an electric field between the gate electrode 170 and the charge zone 160, the electric field having a field strength greater than the coercivity of the third material 131 and less than the coercivity of the second material 121, without substantially changing the polarization direction of the second material.

[0067] For example, the above-described coercivity relationship can be achieved, particularly in embodiments in which the first, second, and third materials have a wurtzite crystal structure, because the third material or third layer has a higher percentage of transition metal than the second material or second layer, e.g., the stated percentage of transition metal in the nitride compound.

[0068] Alternatively or additionally, the above-mentioned relationship between the coercive forces can be achieved in that the third material 131 has a tensile stress. For example, the third layer has a lattice constant that is larger than the reference lattice constant in a direction perpendicular to the major surface of the second layer. The reference lattice constant can be, for example, the equilibrium lattice constant of the third material. The tensile stress can be generated, for example, by a manufacturing process, for example, in the case of deposition, of the third layer in the third material.

[0069] FIG. 2 is a schematic diagram of a further embodiment of the HEMT 100. The HEMT 100 can include a fourth layer 240 disposed between the second layer 120 and the third layer 130. The fourth layer 240 includes a conductive material, such as one of TiN, NbN, Pt, Al, Ti, Mo, and Ni. The fourth layer 240 can be disposed such that the third layer 130 is disposed between the fourth layer 240 and the gate electrode 170. The fourth layer 240 can function as a floating gate. That is, the fourth layer 240 can be potential-free, i.e., cannot be switched to a specific potential. The relationship between the fourth layer 240 and the gate electrode 170 can determine the electric field strength through the third layer. Advantageously, the fourth layer 240 has a larger surface area than the gate electrode 170. Thus, it is possible to achieve a sufficiently high electric field strength through the third layer 130 to change the polarization of the third material, while the electric field strength through the second layer is sufficiently small to prevent breakdown or ferroelectric switching. In this case, the surface area of ​​the fourth layer or gate electrode can refer to an extension in a plane parallel to the layer, i.e., parallel to the major surface of, for example, the first layer 110 or the second layer 120. In other words, the surface measurement of the major surface of the fourth layer 240 arranged opposite the gate electrode can be larger than the surface measurement of the major surface of the gate electrode arranged opposite the fourth layer. In this case, the major surface of the fourth layer can be arranged opposite, for example, parallel to, the major surface of the second layer.

[0070] Thus, in an embodiment, the capacitance between the gate electrode 170 and the fourth layer 240 is less than the capacitance between, for example, the fourth layer 240 and the charge zone 160 when the charge zone is in a conductive state.

[0071] In some embodiments, the HEMT 100 further comprises an insulating layer 250. The implementation of the insulating layer 52 is independent of the implementation of the fourth layer 240. The insulating layer 250 may be disposed between the second layer 120 and the fourth layer 240, as shown in FIG. 2 . In other embodiments, the insulating layer 250 may be implemented without the fourth layer 240. In these embodiments, the insulating layer 250 is disposed between the second layer 120 and the third layer 130. The insulating layer 250 may passivate a further major surface 224 of the second layer 120 opposite the major surface 122. The insulating layer 250 may comprise an electrically insulating material, such as Al2O3, GaN, or AlN.

[0072] In an embodiment, the HEMT 100 further includes an intermediate layer 215. The intermediate layer 215 is disposed between the first layer 110 and the second layer 120. The intermediate layer 215 includes a material made of a nitride compound. The intermediate layer 215 may have a thickness of, for example, less than 10 nm. The intermediate layer 215 can position the charge zone 160 within the first layer 110. The first layer 110 can have particularly low defects, thereby particularly increasing the conductivity of the conduction channel through the charge zone 160 when the charge zone 160 is located within the first layer 110. In an embodiment, the material of the intermediate layer 215 can be one of AlN and GaN. These materials are particularly suitable when the combination of the first material 111 and the second material 121 is any of AlGaN / GaN, AlScN / GaN, and AlScN / GaScN. Intermediate layer 215 can be disposed adjacent to major surface 112 of first layer 110 and adjacent to major surface 122 of second layer 120. In implementations without intermediate layer 215, major surface 112 of first layer 110 can be disposed adjacent to major surface 122 of second layer 120. Intermediate layer 215 can be implemented independently of fourth layer 240 and insulating layer 250.

[0073] In the embodiment shown in FIG. 1, the fourth layer 240, the insulating layer 250, and the intermediate layer 215 can be implemented independently of each other.

[0074] 3 is a schematic diagram of a further embodiment of the HEMT 100. According to this embodiment, the gate electrode 170 and the third layer 130 are part of a gate structure 375. The gate structure 375 is disposed opposite the second layer 120 in the region.

[0075] In the embodiment shown in FIG. 3 , the gate structure 375 is disposed opposite the first region 125 of the first layer 110 and the second layer 120. The first layer 110 and the second layer 120 may further include a second region 127 different from the first region 125. The polarization of the third layer 130 may affect the charge carrier density in the region 161 of the charge zone 160 opposite the gate structure 375. The second region 162 of the charge zone 160 located in the second region 127 of the first layer 110 and / or the second layer 120 may remain largely unaffected by the polarization of the third layer 130 (e.g., aside from edge effects). In the embodiment shown in FIG. 3 , the gate structure 375 further includes a fourth layer 240. However, the gate structure 375 may also be implemented without the fourth layer 240 and / or with an additional insulating layer 250, as shown in FIG. 2 . Optionally, in the embodiment shown in FIG. 3, an intermediate layer 215 may also be implemented.

[0076] In one example implementation of HEMT 100 shown in FIG. 3, first material 111 is intrinsic GaN and second material 121 is Al 0.3 Ga 0.7 N and the third material 131 is AlScN. Optionally, in this embodiment, the material of the fourth layer 240 can be TiN.

[0077] 4 is a schematic diagram of a further embodiment of the HEMT 100. According to the embodiment of FIG. 4, the gate electrode 170 is disposed in the gate electrode region 471, so that the polarization state of the third material 131 in the first region 433 of the third layer 130 opposite the gate electrode 170 can be set by applying a voltage to the gate electrode region 471. The third layer 130 further includes a second region 435 different from the first region 433. The third material in the second region 435 of the third layer 130 is in a polarization state such that the charge zone region 465 of the charge zone 160 opposite the second region 435 is in a conductive state.

[0078] Setting the polarization state of the third material in the first region 433 of the third layer 130 can, for example, set a threshold voltage for the conductivity of the charge zone region 463 of the charge zone 160 opposite the gate electrode 170. Furthermore, the gate electrode 170 can be used to enable or disable a conduction channel through the further charge zone region 463.

[0079] The gate electrode region 471 can extend in a direction (e.g., y-direction) transverse to the direction between the source region 172 and the drain region 174 (e.g., x-direction) completely covering the channel region arranged between the source region 172 and the drain region 174, so that the source region 172 and the drain region 174 are electrically isolated from each other when the further charge zone region 463 is electrically insulating. The surface of the gate electrode 471 can be made, for example, very large precisely so as to be able to disable the conduction channel between the source region 172 and the drain region 174, but can be made as small as possible under this condition to prevent leakage current between the charge zone 160 and the gate electrode 170 and to keep the capacitance of the gate electrode small. At the same time, the distance between the source region 172 and the drain region 174 can be made very large to prevent voltage breakdown, for example, even when the voltage between the source region 172 and the drain region 174, or between the source region 172 and the gate electrode 170, or between the drain region 174 and the gate electrode 170 exceeds 100 V. In an embodiment, the dimension of the gate electrode 170 in the direction from the source region 172 to the drain region 174 is 10% to 80%, or 40% to 60% of the distance between the source region 172 and the drain region 174 .

[0080] 4, the fourth layer 240, the insulating layer 250, and the intermediate layer 215 can be optionally implemented independently of each other. In an embodiment, the fourth layer 240 can be disposed in a region opposite the gate electrode 170.

[0081] The embodiment of HEMT 100 shown in FIGS. 3 and 4 may further comprise source region 172 and drain region 174 as described with reference to FIG.

[0082] FIG. 5 is a schematic diagram of a further embodiment of a HEMT 100. According to this embodiment, the HEMT 100 includes a substrate 106 disposed opposite the first layer 110, such that the first layer 110 is disposed between the substrate 106 and the second layer 120. The substrate 106 may include, for example, Si, SiC, or GaN. The HEMT 100 further includes a multilayer lattice buffer 108 disposed between the substrate 106 and the first layer 110. The lattice buffer 108 may include multiple layers of different materials, including, for example, some or all of GaN, AlGaN, and AlN. The lattice buffer 108 may help create a transition between the lattice constant of the substrate 106 and the lattice constant of the first layer 110, such that the first layer 110 can be fabricated on the substrate 106 with fewer defects. The substrate 106 and lattice buffer 108 may also be implemented in the embodiments shown in FIGS. 1-4.

[0083] In the embodiment shown in FIG. 5, source region 172 and drain region 174 are disposed adjacent to major surface 112 of first layer 110, thereby ensuring electrical contact of source region 172 and drain region 174 to charge zone 160.

[0084] 5 , the gate structure 375 is disposed adjacent to a region of the further major surface 224 of the second layer 120. The HEMT 100 may include a passivation layer 555, which may include an electrically insulating material such as SiN. For example, the passivation layer 555 may be disposed adjacent to a region of the further major surface 224 of the second layer 120 that is not adjacent to the gate structure 375. Furthermore, the passivation layer 555 may be disposed adjacent to the gate structure 375.

[0085] The HEMT 100 may further include a shielding layer 576, which may include a conductive material. The shielding layer 576 may be conductively connected to, for example, the source region 172 or the drain region 174. The shielding layer 576 is disposed opposite the gate electrode 170 such that the gate electrode 170 is disposed between the shielding layer 576 and the second layer 120. Furthermore, an electrically insulating layer, for example, a passivation layer 555, is disposed between the shielding layer 576 and the gate electrode 170. When a voltage is applied between the gate electrode 170 and the source region 172, the shielding layer 576 can shield the gate electrode from the drain region 174 to generate a field effect between the gate electrode 170 and the charge zone 160 electrically connected to the region 120. Furthermore, the shielding layer 576 can ensure the distribution of the electric field of the gate electrode, thereby preventing a strong local electric field and thereby improving the reliability of the component.

[0086] The HEMT 100 can further include a fifth layer 580, which can include an electrically insulating material 580, such as an oxide compound. The fifth layer 580 can be disposed adjacent to the passivation layer 555 and / or the shielding layer 576, such that the passivation layer 555 and / or the shielding layer 576 are disposed between the fifth layer 580 and the second layer 120. For example, the fifth layer 580 can completely cover the area between the source and drain regions. The fifth layer can serve to protect, particularly the shielding layer 576.

[0087] In one example embodiment of the HEMT 100 shown in Figure 5, the substrate 106 is made of Si, SiC, or GaN. The lattice buffer 108 can include a layer of at least GaN, AlGaN, or AlN. The first material 111 can be intrinsic GaN, and the second material can be Al 0.3 Ga 0.7 The third material 131 may be N and the fourth layer 240 may be AlScN. Optionally, the fourth layer 240 may be made of TiN. The passivation layer 555 may be made of SiN, for example.

[0088] 1 and 2, the HEMT 100 may be part of a transistor assembly comprising the HEMT 100 and a control signal generator 190, which is also relevant to the embodiments of Figures 3 to 5. The control signal generator 190 is configured to apply a voltage to the gate electrode 170 to set a polarization direction in a region of the third layer 130 facing the gate electrode 170.

[0089] For example, the control signal generator 190 is configured to set the degree of polarization in the region of the third layer 130 opposite the gate electrode 170 by applying a voltage to the gate electrode 170 to set the threshold voltage of the HEMT 100.

[0090] For example, the control signal generator 190 can be configured to apply a voltage to the gate electrode 170 such that the third material is fully or partially polarized in the region opposite the gate electrode 170 in a manner corresponding to the polarity of the applied voltage, and the magnitude of the applied voltage can determine the degree of polarization, i.e., which portion of the third material is polarized, in the region opposite the gate electrode 170 in a manner corresponding to the polarity of the applied voltage.

[0091] The control signal generator 190 can be configured to apply a first voltage between the gate electrode 170 and the charge zone 160 to set the threshold voltage to a positive value. Additionally, the control signal generator can be configured to apply a second voltage between the gate electrode 170 and the charge zone 160 to set the threshold voltage to a negative value. The control signal generator 190 can, for example, apply a first voltage between the gate electrode 170 and the source region 172 or the drain region 174.

[0092] In the embodiment of the HEMT 100 according to FIGS. 1-5, the polarization state of the third material 131 can be set to increase the threshold voltage of the HEMT. As a result, the HEMT 100 may be suitable, for example, for logic components intended to stably maintain an enabled or disabled state. In an embodiment, the threshold voltage can be set by setting the polarization state of the third material 131 to a positive or negative value, making the HEMT 100 suitable for programmable logic components. Furthermore, the HEMT 100 may enable the implementation of current converters that change their function (e.g., buck and boost) depending on the relationship between the input voltage and the output voltage. In another embodiment, the HEMT 100 may be used in a current converter that can connect or disconnect components depending on the output power.

[0093] 6 is a flow diagram of a method 600 for controlling a HEMT 100 according to one embodiment. The method includes step 601 of applying a voltage to a gate electrode to set a threshold voltage of the HEMT 100 that changes a conduction channel through the charge zone 160 between an enabled and disabled state to set the polarization direction and / or degree of polarization of the third material 131.

[0094] 7 is a flow diagram of a method 700 for controlling a HEMT 100 according to one embodiment. The method includes applying a voltage 701 to the gate electrode 170 to set the polarization direction and / or degree of polarization of the third material 131 such that the threshold voltage of the HEMT 100 that changes the conduction channel through the charge zone 160 between an enabled and disabled state is positive.

[0095] For example, applying 601, 701 a voltage to the gate electrode 170 can be performed in method 600 or 700 by applying a voltage between the gate electrode 170 and the charge zone 160 or by applying a voltage between the gate electrode 170 and the fourth layer 240.

[0096] In an embodiment, the methods 600, 700 of Figures 6 and 7 may further include applying a voltage between the gate electrode 170 and the charge zone 160 to enable or disable a conduction channel through the charge zone 160.

[0097] FIG. 8 is a flow diagram of a method 10 for manufacturing a HEMT according to one embodiment. Method 10 includes step 11, which includes providing a layer structure including a first layer 110, a second layer 120, and a third layer 130. The third layer 130 includes a ferroelectric material 131. The layer structure is provided such that the second layer 120 is disposed between the first layer 110 and the third layer 130, with a major surface 122 of the second layer 120 disposed opposite the major surface 112 of the first layer 110. Furthermore, the layer structure is provided such that a charge zone 160 is formed along the major surface 112 of the first layer 110. This can be achieved, for example, by selecting materials for the first layer 110 and the second layer 120, as described with reference to FIGS. 1-5. Method 10 further includes step 12, which includes applying a source contact 172 and a drain contact 174. Step 12 can be performed, for example, by depositing a metal. The application of source contact 172 and drain contact 174 is performed such that charge zone 160 is disposed electrically in series between the source and drain contacts. Method 10 further includes step 13, which includes temperature treatment, e.g., annealing, of the layer structure together with the source and drain contacts.

[0098] The temperature treatment can achieve or improve ohmic contact between the source contact 172 and the charge zone 160, and between the drain contact 374 and the charge zone 160. For example, the temperature treatment can include exposing the layer structure together with the source and drain contacts to temperatures in excess of 700° C.

[0099] The first layer 110, the second layer 120, and the third layer 130 can be manufactured by the method 10 described with reference to FIGS. 1-5. In particular, the first layer 110, the second layer 120, and the third layer 130 can include the materials described with reference to FIGS. 1-5. In particular, the third layer 130 can include a ferroelectric third material 131. The ferroelectric third material 131 described with reference to FIGS. 1-5 has particularly high temperature stability, so that step 13 can be performed using the layer structure including the third layer 130 without damaging the third layer 130. This is particularly true when the third material 130 is a group-III nitride compound containing a transition metal, such as AlScN.

[0100] Step 11 of providing a layer structure can optionally include providing a layer structure including a first layer 110 and a second layer 120, and the further step of applying a third layer 130. Additionally, step 11 can include structuring the third layer 130. For example, regions of the third layer can be removed to allow application of source contacts 172 and drain contacts 174 in step 12 such that the source contacts 172 and drain contacts 174 are disposed adjacent to the second layer. In other embodiments, step 11 can also include partial removal of the second layer to allow application of source contacts 172 and drain contacts 174 in step 12 such that the source contacts 172 and drain contacts 174 are disposed adjacent to the first layer 110.

[0101] In an embodiment, step 12 further comprises applying a gate electrode 170 .

[0102] Step 12 can be performed such that source contact 172 and drain contact 174, and optionally gate electrode 170, meet the properties and configurations described with reference to FIGS.

[0103] In an embodiment, step 11 includes applying or depositing a first layer 110 on a substrate or on a lattice-adjusting layer on the substrate. Furthermore, step 11 may include applying or depositing a second layer 120 on the first layer 110. Alternatively, step 11 may include applying or depositing an intermediate layer 215 on the first layer 110 and applying or depositing a second layer 120 on the intermediate layer 215, as described with reference to FIGS. 1 to 5, for example. Furthermore, step 11 may include applying or depositing a third layer 130 on the second layer. Alternatively, step 11 may include applying or depositing an insulating layer 250 and / or a fourth layer 240 on the second layer 120 and applying or depositing the third layer 130 on the insulating layer 250 or the fourth layer 240 in a corresponding manner. Step 11 can be performed so that the intermediate layer 215, the fourth layer 240, and the insulating layer 250 meet the properties and arrangements described with reference to FIGS.

[0104] In an embodiment of method 10, step 11 can be performed by method 20 described with reference to FIG.

[0105] FIG. 9 is a flow diagram of a method 20 for fabricating a HEMT according to one embodiment. Method 20 includes step 21, which includes epitaxial deposition of first layer 110 and second layer 120. Step 21 is performed such that major surface 122 of second layer 120 is disposed opposite major surface 112 of first layer 110. Furthermore, step 21 is performed such that charge zones 160 are formed along major surface 112 of first layer 110. This can be achieved by selecting materials for first layer 110 and second layer 120, as described with reference to FIGS. 1-5. Furthermore, method 20 includes step 22, which includes epitaxial deposition of ferroelectric third layer 130. Step 22 is performed such that second layer 120 is disposed between first layer 110 and third layer 130. Steps 21 and 20 are performed such that first layer 110 comprises a first material 111 having a wurtzite crystal structure, second layer 120 comprises a second material 121 having a wurtzite crystal structure, and third layer 130 comprises a ferroelectric third material 131 having a wurtzite crystal structure. As a result, the layer structure comprising first layer 110, second layer 120, and third layer 130 can be deposited particularly well epitaxially.

[0106] Method 20 may include applying a first layer 110, a second layer 120, and a third layer 130 such that they are arranged as described with reference to Figures 1-5. In particular, first layer 110, second layer 120, and third layer 130 may include materials described with reference to Figures 1-5.

[0107] In embodiments, method 20 includes depositing first layer 110, second layer 120, and third layer 120 as described with reference to step 11 of method 10. Method 20 may further include depositing one or more of intermediate layer 215, fourth layer 240, and insulating layer 250, each deposited epitaxially, as described with reference to step 11 of method 10. In these embodiments, advantageously, all layers referred to with reference to step 11 may have a wurtzite crystal structure.

[0108] In particular, the method 10 of FIG. 8 and the method 20 of FIG. 9 can be performed as described with reference to FIGS. 1-5, such that the first layer 110 includes the first material 111, the second layer 120 includes the second material 121, and the third layer 130 includes the third material 131. For example, the combination of the first material 111 and the second material 121 can be any of AlGaN / GaN, AlScN / GaN, AlN / GaN, and AlScN / GaScN. The third material can be a nitride compound or an oxide compound containing zinc. The third material can include one or more group III elements, such as one or more of Al, Ga, or In. Furthermore, the third material 131 can include a transition metal, such as Sc. 、 The third material 131 may include Nb, Ti, or Y. For example, the third material 131 may include one or more group III elements and transition metals, with the fractions optionally being selected as described with reference to FIG. 1 . When the methods 10 and 20 include depositing the fourth layer 240, this may be performed such that the fourth layer includes a conductive material, such as one of TiN, NbN, Pt, Al, Ti, Ni, and Mo. Furthermore, the fourth layer may be epitaxially deposited. When the methods 10 and 20 include depositing the intermediate layer 215, this may be performed such that the intermediate layer 215 includes a material made of a nitride compound, such as one of AlN and GaN.

[0109] While some aspects of the present disclosure are described as device-related features, it will be apparent that such descriptions can also be considered descriptions of corresponding method features. Although some aspects are described as method-related features, it will be apparent that such descriptions can also be considered descriptions of corresponding device features or device functions.

[0110] In the above detailed description, different features may be grouped together in embodiments to rationally explain the disclosure. This type of disclosure is not intended to be interpreted as intending the claimed embodiments to include more features than are expressly specified in each claim. Rather, as the appended claims indicate, subject matter may be formulated with fewer than all features of a single disclosed embodiment. Accordingly, the following claims are incorporated into the detailed description, with all claims considered to be separate and distinct embodiments. While each claim may be considered a separate and distinct embodiment, it should be noted that although a dependent claim may refer to a specific combination with one or more other claims, other embodiments also include combinations of the dependent claim with the subject matter of other dependent claims, or combinations of each feature with other dependent or independent claims. Such combinations are included unless it is stated that a specific combination is not intended. Furthermore, combinations of features from one claim with any other independent claim are also intended to be included, even if the claim does not directly depend on the independent claim.

[0111] The above-described embodiments merely represent examples of the principles of the present disclosure. Naturally, modifications and variations of the configurations and details described herein will be apparent to those skilled in the art. Therefore, it is intended that the present disclosure should be limited only by the scope of protection of the following claims, and not by the specific details presented herein based on the description and illustration of the embodiments.

[0112] References [Hao12] LZ Hao, J. Zhu, YJ Liu, XW Liao, SL Wang, JJ Zhou, C. Kong, HZ Zeng, Y. Zhang, WL Zhang, YR Li, Normally-off characteristics of LiNbO3 / AlGaN / GaN ferroelectric field-effect transistor, Thin Solid Films, 520 (2012) 6313-6317

[0113] [Zhu18] Jiejie Zhu, Lixiang Chen, Jie Jiang, Xiaoli Lu, Ling Yang, Bin Hou, Min Liao, Yichun Zhou, Xiaohua Ma, and Yue Hao, Ferroelectric Gate AlGaN / GaN E-Mode HEMTs With High Transport and Sub-Threshold Performance, IEEE Electron Device Letters, 39 (2018) 79-82

[0114] [Li19] Guanjie Li, Xiaomin Li, Junliang Zhao, Qiuxiang Zhu and Yongbo Chen, Strong interfacial coupling effects of ferroelectric polarization with two-dimensional electron gas in BaTiO3 / MgO / AlGaN / GaN / Si heterostructures, Journal of Materials Chemistry C, 7 (2019) 5677-5685

[0115] [Hao17] Yue Hao; Lixiang Chen; Xiaohua Ma; Jiejie Zhu; Jielong Liu, Doped HfO2 ferroelectric gate dielectric-based AlGaN / GaN enhancement mode HEMT (high electron mobility transistor) device and manufacturing method therefor; CN107316901A, 03.11.2017

[0116] [Yan17] Ling Yang; Lixiang Chen; Xiaohua Ma; Jiejie Zhu; Jielong Liu, Stack gate enhanced GaN high-electron-mobility transistor containing ferroelectric gate dielectric and preparation method; CN107369704 A, 21.11.2017

[0117] [Teo19] Koon Hoo Teo, Nadim Chowdhury, High electron mobility transistor with negative capacitor gate; US 2019 / 0115445 A1 (Apr. 18, 2019)

[0118] [Fic19] Simon Fichtner, Niklas Wolff, Fabian Lofink, Lorenz Kienle, Bernhard Wagner, AlScN: A III-V semiconductor based ferroelectric, Journal of Applied Physics, 125 (2019) 114103

Claims

1. A high electron mobility transistor (HEMT) (100), a first layer (110) comprising a first material (111) consisting of a first nitride compound, said first nitride compound comprising a group III element; a second layer (120) comprising a second material (121) consisting of a second nitride compound, said second nitride compound comprising a group III element; a major surface (122) of the second layer (120) is disposed opposite the major surface (112) of the first layer (110) such that a charge zone (160) is formed along the major surface (112) of the first layer (110) that provides a conduction channel in an effective state of the HEMT; a gate electrode (170) arranged opposite the second layer (120) in at least a region, the second layer (120) being arranged between the first layer (110) and the gate electrode; a third layer (130) disposed between the gate electrode (170) and the second layer (120), the third layer (130) comprising a ferroelectric third material (131) made of a third nitride compound or a ferroelectric third material (131) made of an oxide compound containing zinc, the third material (131) containing a transition metal.

2. The HEMT (100) of claim 1, wherein the third material (131) has a wurtzite crystal structure.

3. The HEMT (100) of claim 2, wherein the first material (111) has a wurtzite crystal structure and the second material (121) has a wurtzite crystal structure.

4. The HEMT (100) of claim 3, wherein the coercivity of the third material is less than the coercivity of the second material.

5. The HEMT (100) of any one of claims 1 to 4, wherein the third material (131) comprises the third nitride compound, the third nitride compound comprising one or more group III elements.

6. The HEMT (100) of claim 5, wherein the one or more group III elements of the third nitride compound are one or more of Al, Ga, and In.

7. The HEMT (100) of any one of claims 1 to 6, wherein the proportion of the transition metal in the third layer is higher than the proportion of the transition metal in the second layer.

8. The HEMT (100) according to any one of the preceding claims, wherein the third material (131) has a tensile stress.

9. The HEMT (100) of any one of claims 1 to 8, wherein the transition metal is Sc, Nb, Ti, or Y.

10. the third material (131) consists of the third nitride compound, the third nitride compound comprises one or more group III elements, and the stoichiometric proportion of the transition metal in the third material (131) is 10% to 50% of the total stoichiometric proportion of the one or more group III elements and the transition metal in the third material (131); or The HEMT (100) according to any one of claims 1 to 9, wherein the third material (131) consists of the oxide compound, and the stoichiometric proportion of the transition metal in the third material (131) is 10% to 50% of the total stoichiometric proportion of the zinc and the transition metal in the third material (131).

11. The HEMT (100) according to any one of claims 1 to 10, wherein the gate electrode (170) and the third layer (130) are part of a gate structure (375) arranged opposite the second layer (120) in an area.

12. The HEMT (100) of any one of claims 1 to 11, further comprising a fourth layer (240) disposed between the second layer (120) and the third layer (130), the fourth layer (240) comprising a conductive material.

13. 13. The HEMT (100) of claim 12, wherein the conductive material of the fourth layer (240) is one of TiN, NbN, Pt, Al, Ti, Ni, and Mo.

14. 14. The HEMT (100) of claim 12 or 13, wherein a capacitance between the fourth layer (240) and the charge zone (160) is greater than a capacitance between the fourth layer (240) and the gate electrode (170).

15. The HEMT (100) according to any one of claims 12 to 14, wherein the gate electrode (170) has a smaller surface relative to a plane parallel to the main surface of the first layer than the fourth layer (240).

16. The HEMT (100) of any one of claims 1 to 15, further comprising an insulating layer (250) disposed between the second layer (120) and the third layer (130), the insulating layer (250) comprising a conductive material.

17. 12. The HEMT (100) of claim 11, wherein the gate structure further comprises a fourth layer (240) disposed between the second layer (120) and the third layer (130), the fourth layer (240) comprising a conductive fourth material.

18. 20. The HEMT (100) of claim 17, wherein the conductive fourth material of the fourth layer (240) is one of TiN, NbN, Pt, Al, Ti, Ni, and Mo.

19. 19. The HEMT (100) of claim 11, 17, or 18, wherein the gate structure further comprises an insulating layer (250) disposed between the second layer (120) and the third layer (130), the insulating layer (250) comprising a conductive material.

20. The HEMT (100) of any one of claims 1 to 19, wherein the combination of the first material (111) and the second material (121) is one of AlGaN / GaN, AlScN / GaN, AlN / GaN, and AlScN / GaScN.

21. The HEMT (100) according to any one of claims 1 to 20, comprising an intermediate layer (215) disposed between the first layer (110) and the second layer (120), the intermediate layer (215) comprising a material made of a nitride compound.

22. 22. The HEMT (100) of claim 21, wherein the material of the intermediate layer (215) is either AlN or GaN.

23. 23. The HEMT (100) of any one of claims 1 to 22, wherein the polarization state of the third material (131) can be set by applying a voltage to the gate electrode (170), and wherein a threshold voltage of the HEMT, which changes a conduction channel through the charge zone (160) between an active state and an inactive state, depends on the polarization state of the third material (131).

24. 24. The HEMT (100) of claim 23, wherein the third material (131) has a first polarization state, and the threshold voltage is positive when the third material (131) is in the first polarization state.

25. 25. The HEMT (100) of claim 24, wherein the third material (131) further has a second polarization state, and wherein the threshold voltage is negative when the third material (131) is in the second polarization state.

26. the gate electrode (170) is disposed within the gate electrode region (471) such that the polarization state of the third material (131) within a first region (433) of the third layer (130) facing the gate electrode region (471) can be set by applying a voltage to the gate electrode (170), the third layer (130) further comprising a second region (435) different from the first region (433); The HEMT (100) of any one of claims 23 to 25, wherein the third material (131) of the second region of the third layer (130) is in a polarization state such that a charge zone region (465) of the charge zone (160) facing the second region is in a conductive state.

27. The HEMT (100) of any one of claims 1 to 26, further comprising a source region (172) and a drain region (174), the charge zone (160) being electrically disposed in series between the source region (172) and the drain region (174).

28. 28. The HEMT (100) of any one of claims 1 to 27, wherein the first material (111) and the second material (121) are semiconducting materials whose bandgaps have a ratio to each other such that an extremum in a potential curve perpendicular to the main surface of the first layer is formed along the main surface (112) of the first layer to provide the charge zone (160).

29. 29. A transistor assembly comprising the HEMT (100) of any one of claims 1 to 28, further comprising a control signal generator (190), the control signal generator (190) configured to apply a voltage to the gate electrode (170) to set a polarization direction in a region of the third layer (130) facing the gate electrode (170).

30. 30. The transistor assembly of claim 29, wherein the control signal generator is configured to set a degree of polarization in the region of the third layer opposite the gate electrode by applying the voltage to the gate electrode to set a threshold voltage of the HEMT.

31. 31. The transistor assembly of claim 30, wherein the control signal generator is configured to apply a first voltage between the gate electrode and the charge zone to set the threshold voltage to a positive value, and to apply a second voltage between the gate electrode and the charge zone to set the threshold voltage to a negative value.

32. A method for controlling a HEMT (100) according to any one of claims 1 to 28, comprising: applying a voltage to the gate electrode to set the polarization direction and / or degree of polarization of the third material (131) to set a threshold voltage of the HEMT (100) that changes a conduction channel through the charge zone (160) between an active state and an inactive state.

33. 33. The method of claim 32, wherein the step of setting the polarization direction and / or the degree of polarization of the third material (131) is performed such that a threshold voltage of the HEMT, which changes a conduction channel through the charge zone (160) between an active state and an inactive state, is positive.

34. A method (10) for manufacturing a HEMT (100), comprising: A step (11) of providing a layer structure comprising a first layer (110), a second layer (120) and a third layer (130), wherein the third layer (130) comprises a ferroelectric third material (131) made of a third nitride compound or a ferroelectric third material (131) made of an oxide compound containing zinc, the third material (131) containing a transition metal; the second layer (120) is disposed between the first layer (110) and the third layer (130); The main surface (122) of the second layer (120) is disposed opposite the main surface (112) of the first layer (110); forming a charge zone (160) along the major surface (112) of the first layer (110) to provide a conduction channel in an effective state of the HEMT; applying (12) a source contact and a drain contact, the charge zone being disposed electrically in series between the source contact and the drain contact; and (13) temperature treating said layer structure together with said source and drain contacts.

35. The step (11) of providing the layer structure comprises: epitaxially applying the first layer (110) and the second layer (120) such that the major surface (122) of the second layer (120) is positioned opposite the major surface (112) of the first layer (110), the charge zone (160) is formed along the major surface (112) of the first layer (110), the first layer (110) comprises a first material (111) having a wurtzite crystal structure, and the second layer (120) comprises a second material (121) having a wurtzite crystal structure; and epitaxially applying (22) the ferroelectric third layer (130) such that the second layer (120) is disposed between the first layer (110) and the third layer (130), the third layer (130) comprising the ferroelectric third material (131) having a wurtzite crystal structure.

36. A method (20) for manufacturing a HEMT (100), comprising: epitaxially applying (21) a first layer (110) and a second layer (120), such that a major surface (122) of the second layer (120) is disposed opposite a major surface (112) of the first layer (110), a charge zone (160) is formed along the major surface (112) of the first layer (110) to provide a conduction channel in an active state of the HEMT, the first layer (110) comprising a first material (111) having a wurtzite crystal structure, and the second layer (120) comprising a second material (121) having a wurtzite crystal structure; epitaxially applying (22) a ferroelectric third layer (130), wherein the second layer (120) is disposed between the first layer (110) and the third layer (130), and the third layer (130) comprises a ferroelectric third material (131) having a wurtzite crystal structure; and applying the ferroelectric third material (131) such that the third material (131) is made of a third nitride or oxide compound containing zinc, the third material (131) containing a transition metal.

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