Patent Description:
The semiconductor industry is driven by its goal to miniaturize integrated electronic circuitry and to increase its switching frequencies and speeds. Conventional, silicon-based integrated circuitry may at some point hit fundamental limits regarding switching frequencies dictated by the capacitance and inductivity of devices and by the energy losses during signal transmission. Concepts for faster circuitry and alternative transmission pathways are desirable. Signal transmission via electromagnetic waves rather than electronic transmission has been proposed. A development from nowadays gigahertz electronics to future terahertz electronics might allow for electronic signal processing and electromagnetic wave signal transmission at similar frequencies using the same or similar integrated electronic elements. Therefore, integrated elements to couple terahertz circuits and the electromagnetic fields are desirable.

Terahertz electromagnetic signal transmission and in particular reception can also be useful for existing applications, such as medical imaging and security screening, or in long scale signal transmission, for example in aerospace industry and space or satellite data communication.

Existing terahertz integrated electronic elements, like resonators required for signal transmission and reception, include split ring and split disc type resonators. The dimensions of these structures are determined by the terahertz wavelength and much larger than the typical, critical dimensions of silicon-based integrated circuitry. Improvements are desirable to allow for the miniaturization and cointegration of terahertz oscillators and resonators with miniaturized integrated circuitry.

<NPL>) describes a ferroelectric-paraelectric system with a periodic domain texture and an average field within a ferroelectric film.

In view of the technical problems described above, there is a need for an improved method for coupling an oscillation in a terahertz spectral range of electrons of an electrical circuit or of a terahertz electromagnetic wave with a resonator, in particular a resonator which can be incorporated into a miniaturized integrated circuit.

This objective is achieved with a method according to independent claim <NUM>. Independent claim <NUM> provides a device with a heterostructure to be applied as a resonator. Independent claim <NUM> provides a method of fabricating a device with a heterostructure suitable to be applied as a resonator. The dependent claims relate to preferred embodiments.

In a first aspect, the disclosure relates to a method of employing a device with a heterostructure as a resonator for electrons of an electrical circuit or for a terahertz electromagnetic wave according to claim <NUM>. The heterostructure comprises a plurality of dielectric layers and a plurality of ferroelectric layers and an alternating stacking sequence of the dielectric layers of the plurality of dielectric layers and the ferroelectric layers of the plurality of ferroelectric layers. The ferroelectric layers comprise a plurality of ferroelectric polarization domains forming a polarization pattern. The polarization pattern is adapted to perform oscillations with a resonance frequency in a terahertz frequency range. The method comprises functionally coupling the oscillation of the polarization pattern and an oscillation of the electrons of the electrical circuit or of the terahertz electromagnetic wave by the device.

The device with the heterostructure can be integrated into miniaturized integrated circuitry, which may provide advantages over existing terahertz resonators such as split ring resonators and split disc resonators. In particular, the lateral area of the device can be miniaturized, for example to the critical dimensions of nowadays' semiconductor devices. Moreover, the plurality of dielectric layers and the plurality of ferroelectric layers can be deposited using well-developed techniques of the layer deposition technology. Advantageously for the miniaturization, elements to provide significant inductance can be omitted in the device.

Advantageously, the plurality of dielectric layers and the plurality of ferroelectric layers may be formed from insulating materials, which may show very little response to oscillations, for example electromagnetic waves, at frequencies much lower or much higher than the resonance frequency, or at the frequencies of the oscillation of the polarization pattern, the electrons of the electrical circuit, or of the terahertz electromagnetic wave. This may suppress undesirable responses and noise which might otherwise result from the response to oscillations, for example electromagnetic waves, at much higher or much lower frequencies.

The resonance frequency may be selected from a plurality of resonance frequencies of the heterostructure and/or of the polarization pattern. In particular, the resonance frequency may correspond to a principal resonance frequency of the plurality of resonance frequencies of the heterostructure and/or of the polarization pattern.

In addition, insulating materials of the at least one ferroelectric layer and/or the at least one dielectric layer may reduce the risk of undesirable electrical short circuiting across the device.

The polarization pattern of the device has a resonance frequency in the terahertz spectral range which can advantageously be adjusted to the requirements of a specific application, for example by selecting suitable thicknesses of the at least one ferroelectric layer or the at least one dielectric layer, or by selecting a suitable material composition of the at least one ferroelectric layer and the at least one dielectric layer. The resonance frequency can advantageously be used for resonant coupling between the oscillation of the polarization pattern and the oscillation of the electrons of the electrical circuit or of the terahertz electromagnetic wave. Resonant coupling provides a particularly efficient coupling.

In the context of the present disclosure, the terahertz frequency range may comprise frequencies of at least <NUM> THz, in particular at least <NUM> THz or at least <NUM> THz.

In the context of the present disclosure, the terahertz frequency range may comprise frequencies up to <NUM> THz, in particular up to <NUM> THz or up to <NUM> THz.

The oscillation of the polarization pattern can have an oscillation frequency in a second terahertz frequency range.

The oscillation of the electrons of the electrical circuit or of the terahertz electromagnetic wave can have a coupling frequency in the second terahertz frequency range.

The second terahertz frequency range may comprise frequencies of at least <NUM> THz, in particular at least <NUM> THz or at least <NUM> THz.

The second terahertz frequency range may comprise frequencies up to <NUM> THz, in particular up to <NUM> THz or up to <NUM> THz.

The oscillation of the polarization pattern and/or the oscillation of the electrical circuit or of the terahertz electromagnetic wave with an oscillation frequency or a coupling frequency not too far from the resonance frequency of the polarization pattern may advantageously allow for efficient coupling between the oscillation of the polarization pattern and the oscillation of the electrical circuit or of the terahertz electromagnetic wave.

The oscillation of the polarization pattern may have an oscillation frequency, and the oscillation of the electrons of the electrical circuit or of the terahertz electromagnetic wave may have a coupling frequency, and the coupling frequency may match the oscillation frequency. According to an embodiment of the disclosure, the oscillation frequency matches the resonance frequency.

The resulting resonant coupling can allow for a particularly efficient coupling between the oscillation of the polarization pattern and the oscillation of the electrons of the electrical circuit or of the terahertz electromagnetic wave.

According to an embodiment, the coupling frequency matches the resonance frequency.

Matching frequencies may deviate from one another at most by a factor of <NUM>, in particular at most <NUM>, or at most <NUM>.

According to an embodiment, the plurality of ferroelectric layers may comprise at least three ferroelectric layers, in particular at least five, ten, twenty, or fifty ferroelectric layers.

Each ferroelectric layer of the plurality of ferroelectric layers may comprise a plurality of ferroelectric polarization domains forming a polarization pattern.

According to an embodiment, each layer of the plurality of ferroelectric layers may have a same maximum ferroelectric layer thickness. In particular, each layer of the plurality of ferroelectric layers may have a same ferroelectric layer thickness, for example along a line intersecting the heterostructure, in particular along a line intersecting the heterostructure along a direction perpendicular to the at least one ferroelectric layer.

Alternatively or in addition, the plurality of dielectric layers may comprise at least three dielectric layers, in particular at least five, ten, twenty, or fifty dielectric layers.

According to an embodiment, each layer of the plurality of dielectric layers may have a same maximum dielectric layer thickness. In particular, each layer of the plurality of dielectric layers may have a same dielectric layer thickness, for example along a line intersecting the heterostructure, in particular along a line intersecting the heterostructure along a direction perpendicular to the at least one dielectric layer.

Alternatively or in addition, the heterostructure may comprise a stacking sequence with at least one additional layer between a first layer of the plurality of ferroelectric layer or of the plurality of dielectric layers and a second layer of the plurality of the plurality of ferroelectric layer or of the plurality of dielectric layers.

A plurality of ferroelectric layers and/or a plurality of dielectric layers can increase the coupling volume and hence the strength of the coupling between the oscillation of the polarization pattern and the oscillation of the electrical circuit or of the terahertz electromagnetic wave.

According to an embodiment, the method further comprises employing the device as a component of a receiver or a transmitter for the terahertz electromagnetic wave.

Employing the device as a component of the receiver or the transmitter advantageously makes use of the coupling between the oscillation of the polarization pattern and the coupling of the electrons of the electrical circuit. This may be particularly useful for applications of the device related to inter-chip and/or intra-chip signal transmission and/or processing, <NUM> WiFi communication, and/or satellite communication.

According to an embodiment, the heterostructure is functionally coupled to a diode or a transistor. In particular, the device may be a component of the receiver, and the diode or the transistor serves as a rectifier.

As the device with the heterostructure can be integrated together with miniaturized semiconductor devices like the transistor and/or the diode, these well-established semiconductor devices can advantageously be used to implement a driver and/or a readout circuit for the resonator.

According to an embodiment, the device is a first component of a common integrated circuit and the diode or the transistor is a second component of the common integrated circuit. For example, the first component of the common integrated circuit and the second component of the common integrated circuit may be arranged on a common substrate. For example, the common substrate may be a semiconductor or dielectric substrate. In particular, the semiconductor or dielectric substrate may be a semiconductor or dielectric wafer.

According to an embodiment, the first component of the common integrated circuit and the second component of the common integrated circuit are arranged in direct physical contact with each other.

At least a layer of the device and at least a section of the second component of the common integrated circuit may be composed of the same material. The same material composition of the layer of the device and the section of the second component of the common integrated circuit may by the result of a common deposition step.

The device may be functionally coupled to an additional antenna. In particular, the additional antenna may be a split ring resonator or a split disc resonator.

According to an embodiment, the method further comprises applying the device as a component of an RC circuit. In particular, the device may be employed as a capacitor of the RC circuit.

The implementation of an RC circuit comprising the device provides a resonator with the potential to be highly miniaturized and integrated. In particular, the implementation as an RC circuit permits to omit significant inductances, which tend to require large lateral areas is in the layout of an integrated circuit.

The RC circuit may comprise a resistor in parallel or in series with the heterostructure. According to an embodiment, the device is a first component of a common integrated circuit, and the resistor is a second component of the common integrated circuit.

The device and a resistor can advantageously be formed as components of a common integrated circuit.

The common integrated circuit, the first component of the common integrated circuit, and the second component of the common integrated circuit may be characterized by features corresponding to the ones described in the context of a diode or a transistor forming the second component of the common integrated circuit.

The device may be employed as a component of a low pass filter, a high pass filter, or a band pass filter.

In particular, the RC circuit comprising the device as a component may be employed as a component of a low pass filter, a high pass filter, or a band pass filter.

The low pass filter, the high pass filter, or the band pass filter can have a cutoff frequency in a cutoff frequency range.

The band pass filter can have a second cutoff frequency in the cutoff frequency range.

The cutoff frequency range may comprise frequencies of at least <NUM> THz, in particular at least <NUM> THz or at least <NUM> THz.

The cutoff frequency range may comprise frequencies up to <NUM>,<NUM> THz, in particular up to <NUM> THz.

The low pass filter, the high pass filter, or the band pass filter may be an electronic low pass filter, an electronic high pass filter, or an electronic band pass filter.

The device may be employed as a component of a clock.

The device advantageously provides a resonance frequency in the terahertz frequency range, which is just above the frequency range being used by current electronics, and thus may permit to implement clocks operating at higher frequency and thus at higher precisions than the ones currently used in semiconductor devices.

Employing the device as a component of the clock may comprise determining a maximum or a minimum of a parameter that characterizes the oscillation of the polarization pattern.

Employing the device as a component of the clock may comprise counting a plurality of maxima or minima, wherein each maximum or minimum is a maximum or a minimum of the parameter related to the oscillation of the polarization pattern.

The parameter related to the oscillation of the polarization pattern may be a measure of the total polarization of the polarization pattern or a measure of the change of the total polarization of the polarization pattern.

The parameter related to the oscillation of the polarization pattern may be a measure of a local polarization of the polarization pattern, or a measure of the change of a local polarization of the polarization pattern.

The device may further comprise a second heterostructure comprising at least one second dielectric layer and at least one second ferroelectric layer. The second ferroelectric layer may comprise a second plurality of ferroelectric polarization domains forming a second polarization pattern, and the second polarization pattern may be adapted to perform a second oscillation with a second resonance frequency in the terahertz frequency range. Applying the device may further comprise employing the heterostructure as a component of a transmitter adapted to generate a transient terahertz electromagnetic wave, and employing the second heterostructure as a component of a receiver to receive the transient terahertz electromagnetic wave. This may be particularly useful for applications of the device related to intra-chip signal transmission and/or processing.

The second heterostructure may comprise a second plurality of ferroelectric layers. The plurality of ferroelectric layers may comprise at least three ferroelectric layers, in particular at least five, ten, twenty, or fifty ferroelectric layers.

According to an embodiment, the at least one second ferroelectric layer may be at least one ferroelectric layer of the second plurality of ferroelectric layers. The at least one second ferroelectric layer may be or comprise a thickest ferroelectric layer of the second plurality of ferroelectric layers, or a thinnest ferroelectric layer of the second plurality of ferroelectric layers.

In particular, each layer of the second plurality of ferroelectric layers may have a same second maximum ferroelectric layer thickness. In particular, each layer of the second plurality of ferroelectric layers may have a same second ferroelectric layer thickness, for example along a line intersecting the second heterostructure, in particular along a line intersecting the second heterostructure along a direction perpendicular to the second ferroelectric layer.

Alternatively, or in addition, the second heterostructure may comprise a second plurality of dielectric layers. The plurality of dielectric layers may comprise at least three ferroelectric layers, in particular at least five, ten, twenty, or fifty dielectric layers.

According to an embodiment, the at least one second dielectric layer may be a dielectric layer of the second plurality of dielectric layers. The at least one second dielectric layer may be or comprise a thickest dielectric layer of the second plurality of dielectric layers, or a thinnest dielectric layer of the second plurality of dielectric layers.

In particular, each layer of the second plurality of dielectric layers may have a same second maximum dielectric layer thickness. In particular, each layer of the second plurality of dielectric layers may have a same second dielectric layer thickness, for example along a line intersecting the second heterostructure, in particular along a line intersecting the second heterostructure along a direction perpendicular to the at least one second dielectric layer.

According to an embodiment, the heterostructure is a first component of a common integrated circuit, and the second heterostructure is a second component of the common integrated circuit.

The method may further comprise guiding the transient terahertz electromagnetic wave using a waveguide structure.

The method may further comprise guiding the transient terahertz electromagnetic wave using a metallic channel, in particular a metallic channel serving as a plasmonic interconnect channel.

A waveguide structure and/or a plasmonic interconnect channel may be particularly useful for applications of the device related to intra-chip signal transmission and/or processing.

The method may further comprise using the device as a component of a terahertz optical device to manipulate the terahertz electromagnetic wave and to control at least one terahertz optical parameter.

For example, the terahertz optical device may be a mirror to reflect the terahertz electromagnetic wave, and the terahertz optical parameter may be a reflectance.

For example, the terahertz optical device may be an attenuator to transmit a portion of the terahertz electromagnetic wave, and the terahertz optical parameter may be an attenuation.

For example, the terahertz optical device may be a beam splitter to reflect a portion of the terahertz electromagnetic wave and to transmit another portion of the terahertz electromagnetic wave, wherein the terahertz optical parameter is a reflectance and a second terahertz optical parameter may be a transmittance.

For example, the terahertz optical device may be a phase shifter to modify a phase of the terahertz electromagnetic wave, and the terahertz optical parameter may be a phase shift.

For example, the terahertz optical device may be a terahertz optical low pass filter, a terahertz optical high pass filter, or a terahertz optical bandpass filter for the terahertz electromagnetic wave, and the terahertz optical parameter may be a cutoff frequency.

Advantageously, techniques for the design of layered dielectric optics can be used to tailor the terahertz optical device to match the requirements of specific application, for example as a mirror, a beam splitter, an attenuator, a phase shifter, a dichroic mirror, a (terahertz) optical high pass filter, a (terahertz) optical low pass filter, a (terahertz) band pass filter, or as a (terahertz) optical notch filter.

For example, the terahertz optical device may be a guiding structure for the terahertz electromagnetic wave, and the terahertz optical parameter may be a direction of the terahertz electromagnetic wave. In particular, the terahertz optical device may comprise a terahertz optical metamaterial to guide the terahertz electromagnetic wave inside the heterostructure.

A thickness of the at least one ferroelectric layer may be adapted to control the terahertz optical parameter.

The method may further comprise applying a static electric field to the heterostructure to control the terahertz optical parameter.

The method may further comprise triggering the oscillation of the electrons of the electrical circuit to control the terahertz optical parameter.

The method may further comprise applying a mechanical stress to the heterostructure to control the terahertz optical parameter.

The heterostructure may be a first component of a common integrated circuit, and an additional terahertz optical device or an additional terahertz optoelectronic device may be a second component of the common integrated circuit.

The common integrated circuit, the first component of the common integrated circuit, and the second component of the common integrated circuit may be characterized by features corresponding to the ones described in the context of a diode or a transistor as the second component of the common integrated circuit.

The method may further comprise employing the device as a component of a receiver or a transmitter for the terahertz electromagnetic wave, in addition to using the device as a component of a terahertz optical device to manipulate the terahertz electromagnetic wave and to control at least one terahertz optical parameter.

In a second aspect, the disclosure relates to a device according to claim <NUM>.

The device with the heterostructure can advantageously be applied in a method comprising at least some of the features described above.

The terahertz frequency range and/or the second terahertz frequency range may be defined as in the context of the first aspect of the disclosure.

The plurality of ferroelectric layers may comprise at least three ferroelectric layers, in particular at least five, ten, twenty, or fifty ferroelectric layers.

In particular, each layer of the plurality of ferroelectric layers may have a same maximum ferroelectric layer thickness. In particular, each layer of the plurality of ferroelectric layers may have a same ferroelectric layer thickness, for example along a line intersecting the heterostructure, in particular along a line intersecting the heterostructure along a direction perpendicular to the at least one ferroelectric layer.

Alternatively, or in addition, the plurality of dielectric layers may comprise at least three dielectric layers, in particular at least five, ten, twenty, or fifty dielectric layers.

In particular, each layer of the plurality of dielectric layers may have a same maximum dielectric layer thickness. In particular, each layer of the plurality of dielectric layers may have a same dielectric layer thickness, for example along a line intersecting the heterostructure, in particular along a line intersecting the heterostructure along a direction perpendicular to the at least one dielectric layer.

The heterostructure can have a height of at least <NUM>, in particular of at least <NUM>, in particular of at least <NUM>, in particular of at least <NUM>.

The heterostructure may cover a lateral area of at most <NUM><NUM>, in particular of at most <NUM><NUM>, in particular of at most <NUM><NUM>, or of at most <NUM><NUM>, or at most <NUM><NUM>.

The polarization pattern may have a spatial periodicity along a lateral direction of the at least one ferroelectric layer. In particular, the polarization pattern may be a periodic polarization pattern. According to an embodiment, a thickness of the at least one ferroelectric layer does not exceed <NUM>, in particular <NUM>, <NUM>, <NUM> or <NUM>.

In general, several or all ferroelectric layers of the plurality of ferroelectric layers may have an identical thickness. In other embodiments, a thickness of several or all ferroelectric layers of the plurality of ferroelectric layers may differ.

In embodiments with a plurality of ferroelectric layers, a thickness of some or any of the ferroelectric layers comprised in the plurality of ferroelectric layers may not exceed <NUM>, in particular <NUM>, <NUM>, <NUM> or <NUM>.

The plurality of ferroelectric layers may comprise lead titanate, barium titanate, zirconium oxide or hafnium oxide. The first ferroelectric layer of the plurality of ferroelectric layers and a second ferroelectric layer of the plurality of ferroelectric layers may be composed of the same material or of different materials.

According to an embodiment, a thickness of the at least one dielectric layer comprised in the plurality of dielectric layers does not exceed <NUM>, in particular <NUM>, <NUM>, <NUM> or <NUM>. In general, several or all dielectric layers of the plurality of dielectric layers may have an identical thickness. In other embodiments, a thickness of several or all dielectric layers of the plurality of dielectric layers may differ.

In embodiments with a plurality of dielectric layers, a thickness of some or any of the dielectric layers comprised in the plurality of dielectric layers may not exceed <NUM>, in particular <NUM>, <NUM>, <NUM> or <NUM>.

The plurality of dielectric layers may comprise insulating material.

In embodiments with a plurality of dielectric layers, a first dielectric layer of the plurality of dielectric layers and a second dielectric layer of the plurality of dielectric layers may be composed of the same material, or of different materials.

The device further comprises a bottom electrode arranged below the heterostructure. In particular, the bottom electrode may be arranged below the plurality of dielectric layers and/or below the plurality of ferroelectric layers.

The device further comprises a top electrode arranged above the heterostructure. In particular, the top electrode may be arranged above the plurality of dielectric layers and/or above the plurality of ferroelectric layers.

The device may further comprise at least one intermediate electrode arranged between an intermediate top layer and an intermediate bottom layer.

In embodiments with a heterostructure comprising one dielectric layer and one ferroelectric layer, the intermediate top layer may be the ferroelectric layer or the dielectric layer, and the intermediate bottom layer may be the dielectric layer or the ferroelectric layer, respectively.

The intermediate bottom layer may be a dielectric layer from the plurality of dielectric layers, and/or the intermediate top layer may be a dielectric layer from the plurality of dielectric layers.

The intermediate bottom layer may be a ferroelectric layer from the plurality of ferroelectric layers, and/or the intermediate top layer may be a ferroelectric layer from the plurality of ferroelectric layers.

The structure and material composition of the intermediate electrode may generally correspond to those of the bottom electrode and top electrode described above.

An intermediate electrode located within the heterostructure may allow for more versatile application of the resonator.

Each of the bottom electrode, top electrode and bottom electrode may be adapted to be connected to an external driving circuitry, or to ground.

The heterostructure may be arranged above a substrate.

The substrate may be structured to promote the formation of the device. Advantageously, additional elements may be formed on the same device to implement complex integrated circuitry. Moreover, the device may be selected to promote the formation of at least one layer of the device, for example via the wetting properties of the substrate or via epitaxial growth of at least one layer of the device on the substrate.

The substrate may be a semiconductor or dielectric substrate.

Semiconductor or dielectric substrates are well developed, available at moderate pricing, and the formation of a layer on semiconductor or dielectric substrates has been highly developed in the context of layer deposition technology.

The substrate may comprise a single crystalline section with a lateral dimension at least as large as a lateral dimension of the heterostructure. In particular, the substrate may be adapted to promote epitaxial growth of the at least one dielectric layer or of the at least one ferroelectric layer. Crystalline sections of the substrate may promote epitaxial growth of at least one layer of the device. Epitaxial growth tends to minimize the density of defects in the layer.

The device may be a mechanically flexible device.

In particular, the device may be a free-standing device.

The device may further comprise an additional integrated element, wherein the heterostructure is a first component of a common integrated circuit, and the additional integrated element is a second component of the common integrated circuit.

The common integrated circuit, the first component of the common integrated circuit, and the second component of the common integrated circuit may be characterized by features corresponding to the ones described in the context of the method with a diode or a transistor as the second component of the common integrated circuit.

For example, the additional integrated element may be a resistor. The resistor may be arranged in series or in parallel with the heterostructure.

For example, the additional integrated element may be a diode or a transistor. The diode or transistor may be functionally coupled to the heterostructure.

For example, the additional integrated element may be an additional terahertz optical device or an additional terahertz optoelectronic device.

For example, the additional integrated element may be an additional antenna coupled to the heterostructure.

In particular, the additional antenna may be a split ring resonator or a split disc resonator.

The device may further comprise a plurality of integrated elements, wherein each integrated element of the plurality of integrated elements may be a component of the common integrated circuit.

The device may further comprise a second heterostructure adapted to be applied as a second resonator for electrons of a second electrical circuit or for a second terahertz electromagnetic wave. The second heterostructure may comprise at least one dielectric layer and at least one second ferroelectric layer. The at least one second ferroelectric layer may comprise a second plurality of ferroelectric polarization domains forming a second polarization pattern. The second polarization pattern may be adapted to execute a second oscillation with a second resonance frequency in the terahertz frequency range. The device may be adapted to couple the second oscillation of the second polarization pattern with a third oscillation at a second coupling frequency of the electrons of the second electrical circuit or of the second terahertz electromagnetic wave. The second oscillation of the second polarization pattern may have a second oscillation frequency in the second terahertz frequency range.

In some embodiments, the design and features of the second heterostructure may correspond to those of the heterostructure described above, such as in terms of the layout, the number and position of the ferroelectric layers and the dielectric layers, the layer thicknesses and material composition.

In particular, the at least one second ferroelectric layer may be at least one ferroelectric layer of the second plurality of ferroelectric layers. The at least one second ferroelectric layer may be or comprise a thickest ferroelectric layer of the second plurality of ferroelectric layers, or a thinnest ferroelectric layer of the second plurality of ferroelectric layers.

According to an embodiment, each layer of the second plurality of ferroelectric layers may have a same second maximum ferroelectric layer thickness. In particular, each layer of the second plurality of ferroelectric layers may have a same second ferroelectric layer thickness, for example along a line intersecting the second heterostructure, in particular along a line intersecting the second heterostructure along a direction perpendicular to the at least one second ferroelectric layer.

In particular, the at least one second dielectric layer may be at least one dielectric layer of the second plurality of dielectric layers. The at least one second dielectric layer may be or comprise a thickest dielectric layer of the second plurality of dielectric layers, or a thinnest dielectric layer of the second plurality of dielectric layers.

According to an embodiment, each layer of the second plurality of dielectric layers may have a same second maximum dielectric layer thickness. In particular, each layer of the second plurality of dielectric layers may have a same second dielectric layer thickness, for example along a line intersecting the second heterostructure, in particular along a line intersecting the second heterostructure along a direction perpendicular to the at least one second dielectric layer.

The second resonance frequency may be selected from a second plurality of resonance frequencies of the second heterostructure and/or of the second polarization pattern.

In particular, the second resonance frequency may correspond to a principal resonance frequency of the second plurality of resonance frequencies of the second heterostructure and/or of the second polarization pattern.

The second resonance frequency may match the resonance frequency.

The second terahertz electromagnetic wave and the terahertz electromagnetic wave may be identical, and the device may be adapted to couple the oscillation of the polarization pattern and the second oscillation of the second polarization pattern using the terahertz electromagnetic wave.

In a third aspect, the disclosure relates to a method of fabricating a device with a heterostructure according to claim <NUM>.

The device with the heterostructure is suitable to be applied as a resonator for electrons of an electrical circuit or for a terahertz electromagnetic wave.

The method may further comprise depositing at least three ferroelectric layers, in particular at least five, ten, twenty, or fifty ferroelectric layers.

According to an embodiment, each layer of the plurality of ferroelectric layers may be deposited with a same ferroelectric layer thickness, for example along a line intersecting the heterostructure, in particular along a line intersecting the heterostructure along a direction perpendicular to the at least one ferroelectric layer.

Alternatively, or in addition, the method may comprise depositing a plurality of dielectric layers may comprise depositing at least three dielectric layers, in particular at least five, ten, twenty, or fifty dielectric layers.

According to an embodiment, each layer of the plurality of dielectric layers may be deposited with a same dielectric layer thickness, for example along a line intersecting the heterostructure, in particular along a line intersecting the heterostructure along a direction perpendicular to the at least one dielectric layer.

The predefined maximum thickness may comprise a largest thickness of the at least one ferroelectric layer along a lateral direction of the heterostructure.

The predefined maximum thickness may comprise the largest thickness of the at least one ferroelectric layer in a volume between the top electrode and the bottom electrode.

In embodiments with a plurality of ferroelectric layers, the predefined maximum thickness may be a thickness of a thickest ferroelectric layer of the plurality of ferroelectric layers along a line intersecting the heterostructure, in particular along a line perpendicular to the plurality of ferroelectric layers.

In embodiments with a top electrode and a bottom electrode and a plurality of ferroelectric layers, the predefined maximum thickness may comprise a thickness of a thickest ferroelectric layer of the plurality of ferroelectric layers along a line connecting the bottom electrode and the top electrode, in particular a line perpendicular to the bottom electrode and the top electrode. Alternatively, or in addition, the method may comprise adjusting a ratio of the ferroelectric layer thickness and a dielectric constant of the at least one ferroelectric layer.

The terahertz frequency range may comprise frequencies of at least <NUM> THz, in particular at least <NUM> THz or at least <NUM> THz.

The terahertz frequency range may comprise frequencies up to <NUM> THz, in particular up to <NUM> THz or up to <NUM> THz.

According to an embodiment, adjusting the predefined maximum thickness comprises selecting the predefined maximum thickness in accordance with a material constant of a material comprised in the at least one ferroelectric layer. In particular, the material constant of the material comprised in the at least one ferroelectric layer may be the dielectric constant of the material comprised in the at least one ferroelectric layer.

Adjusting the predefined maximum thickness may comprise selecting the predefined maximum thickness in accordance with a lateral area of the at least one ferroelectric layer.

Adjusting the predefined maximum thickness may comprise selecting the predefined maximum thickness in accordance with a dielectric constant of a material comprised in the at least one dielectric layer.

Adjusting the predefined maximum thickness may comprise selecting the predefined maximum thickness in accordance with a thickness of the at least one dielectric layer.

Adjusting the predefined maximum thickness may comprise selecting the predefined maximum thickness in accordance with a number of the dielectric layers and/or a number of the ferroelectric layers.

Adjusting the predefined maximum thickness may comprise selecting the predefined maximum thickness in accordance with an average size of the ferroelectric polarization domains. Adjusting the predefined maximum thickness may comprise selecting the predefined maximum thickness in accordance with a size distribution of the ferroelectric polarization domains.

The present disclosure relates to a device with a heterostructure comprising a plurality of ferroelectric layers. The device may provide a strong frequency dependence of the dielectric permittivity within a terahertz (THz) frequency range.

The terahertz frequency is not uniquely defined, and in the context of the present disclosure may be understood to start at a frequency of <NUM> THz, in particular <NUM> THz or <NUM> THz. Correspondingly, the terahertz frequency range may comprise frequencies up to <NUM> THz, in particular up to <NUM> THz or up to <NUM> THz. According to one possible definition, a THz spectral range may correspond to wavelengths in a range from <NUM> to <NUM>. The terahertz electromagnetic spectrum may generally be understood to lie between microwaves and far infrared.

The device with a heterostructure according to claim <NUM> will in the following be explained by way of the example of a Terahertz Ferroelectric Resonator (TFR).

<FIG> illustrates an example of a TFR <NUM>. The exemplary TFR <NUM> comprises a heterostructure, which may be a sandwich-like heterostructure, a multilayer structure, or a superlattice. The heterostructure may be deposited, for instance, on a dielectric or semiconductor substrate <NUM>. The TFR <NUM> comprises an alternating sequence of layers, including a plurality of dielectric layers <NUM> and a plurality of ferroelectric layers <NUM>. The example TFR <NUM> of <FIG> comprises six dielectric layers <NUM> and five ferroelectric layers <NUM>, but other embodiments of the TFR <NUM> may comprise different numbers of layers, for example one ferroelectric layer and one dielectric layer, or any other number of ferroelectric layers and/or dielectric layers, depending on the application.

The heterostructure of the TFR <NUM> can be realized, for example, as an epitaxial grown superlattice wherein one, several or all of the dielectric layers <NUM> are mostly composed of SrTiO<NUM> perovskite oxide and one, several or all the ferroelectric layers <NUM> are mostly composed of PbTiO<NUM> perovskite oxide. Alternatively, the ferroelectric layers <NUM> may for example comprise other oxides with the perovskite structure, such as barium titanate or lead zirconium titanate, or non-perovskite oxides, such as zirconium oxide or hafnium oxide, in particular doped hafnium oxide. Other material compositions, comprising, for example, halides, are possible.

A typical thickness hd of an individual layer of the dielectric layers <NUM> and typical thickness hf of the ferroelectric layers <NUM> can be in a range from a few nm to tens of nm. The number of dielectric layers <NUM> and the number of ferroelectric layers <NUM> can vary from a few to tens to hundreds or even more. In the example, the overall thickness H of the dielectric layers <NUM> and ferroelectric layers <NUM>, and the lateral area of the device, which may be related to the area of the top surface S of the device, do not exceed the characteristic terahertz wavelength in the heterostructure <MAT> (with the dielectric constant ε ≃ <NUM> and λ ≃ <NUM>µm for the wavelength of an electromagnetic wave with the frequency of <NUM> THz terahertz in vacuum) to avoid parasite inductivity.

The ferroelectric material possesses ferroelectric polarization domains <NUM>, <NUM> with uniaxial anisotropy of the polarization, which may either occur naturally or be strain-induced and/or be tailored by strain engineering. For this purpose, an epitaxial relationship between the dielectric layers <NUM> in the ferroelectric layers <NUM> may be useful, although not necessary. Moreover, a dielectric relationship between the dielectric layer <NUM> or the ferroelectric layers <NUM> and the substrate <NUM> may be useful, but not necessary.

According to the example depicted in <FIG>, the polarization of the ferroelectric polarization domains <NUM>, <NUM> is directed along the z-axis, which is defined along the surface normal of the layers of the heterostructure. Other orientations of the polarization are, however, possible.

The ferroelectric layers <NUM> of the heterostructure of <FIG> are insulating, and the heterostructure is insulating. It is confined in between a bottom electrode <NUM> and a top electrode <NUM>. Each of the bottom electrode <NUM> and the top electrode <NUM> can have a thickness in the range from <NUM> to <NUM> and comprises metallic or semiconducting material. The combination of the bottom electrode <NUM>, the top electrode <NUM>, and the heterostructure with the dielectric layers <NUM> and the ferroelectric layers <NUM> can be viewed as an effective capacitor. The TFR <NUM> can for example be produced by subsequent and/or alternating deposition of the dielectric layers <NUM> and the ferroelectric layers <NUM> on the substrate <NUM>. In this case, the bottom electrode <NUM> is deposited on the substrate <NUM> prior to the deposition of the heterostructure. Consequently, at least a portion of the bottom electrode <NUM> is arranged between the substrate <NUM> and the heterostructure of the TFR <NUM>. The top electrode <NUM> can be fabricated above the heterostructure in an additional deposition process after the deposition of the heterostructure. A bottom contact <NUM> can be attached to the bottom electrode <NUM>, and a top contact <NUM> can be attached to the top electrode <NUM> for implementation of the electrical connection with an external circuit.

<FIG> illustrates the electronic graphical symbol <NUM> for the TFR <NUM>.

A peculiarity of the alternating combination of the dielectric layers <NUM> and ferroelectric layers <NUM> is that the polarization of each ferroelectric layer <NUM> terminates at the corresponding dielectric-ferroelectric interfaces and creates interface depolarization charges. The interface depolarization charges are positive at the head of the polarization termination, corresponding to a dielectric-ferroelectric interface of an individual ferroelectric layer <NUM> of the heterostructure, and negative at its tail, corresponding to the opposite dielectric-ferroelectric interface of the same individual ferroelectric layer <NUM> of the heterostructure. The interface depolarization charges cause depolarization fields. The depolarization fields induced by the interface depolarization charges are energetically costly. This leads to the formation of ferroelectric polarization domains forming a polarization pattern. The polarization pattern may have a spatial periodicity along one or both lateral directions of the film.

<FIG> show examples of periodic polarization patterns of heterostructures <NUM>, <NUM>. The heterostructure <NUM> in <FIG> has a periodic polarization pattern with stripes. The heterostructure <NUM> in <FIG> has a cylindrical, or bubble-like, periodic polarization pattern. For example, if the ferroelectric layers <NUM> are composed of PbTiO<NUM>, the periodic polarization pattern of <FIG> may have a periodicity of <NUM>-<NUM> of the ferroelectric polarization domains <NUM>, <NUM>. The periodic polarization pattern and the resulting reduction of the depolarization charges of the ferroelectric polarization domains <NUM>, <NUM> can substantially reduce the electrostatic energy related to the depolarization charges.

The polarization pattern, for example the periodic polarization patterns of heterostructures <NUM>, <NUM> of <FIG>, can perform an oscillation. The coupling of the oscillation of the polarization pattern with a sub-THz to THz signal constitutes an important aspect of the disclosure. Here, the sub-THz to THz signal may have a frequency in a terahertz frequency range. The terahertz frequency range of the sub-THz to THz signal may correspond to the terahertz frequency range of the resonance frequency to promote resonant coupling, or may be a wider frequency range in case of non-resonant coupling. The sub-THz to THz signal may be or may be related to an oscillation of electrons of an electrical circuit or to an oscillation of a terahertz electromagnetic wave.

On the structural level, the oscillation of the ferroelectric polarization domains <NUM>, <NUM>, or the oscillation of the polarization pattern, respectively, may be related to a dynamical vibration mode of a periodic polarization pattern with a resonance frequency. In particular, the oscillation of the ferroelectric polarization domains <NUM>, <NUM>, or the oscillation of the polarization pattern, respectively, may be related to an oscillation of the total polarization or to an oscillation of the local polarization. The oscillation of the polarization pattern can be coupled with the sub-THz to THz signal.

The disclosure may, but does not necessarily, advantageously make use of resonant coupling to achieve a strong and efficient coupling between the oscillation of the polarization pattern and the sub-THz to THz signal. Resonant coupling occurs when the frequency of the sub-THz to THz signal matches a resonance frequency. In this context, matching may refer to a matching within a factor of <NUM>, in particular within a factor of <NUM> or <NUM>.

In situations where the sub-THz to THz signal is a terahertz electromagnetic wave with a wavelength of <NUM>-<NUM>, the terahertz wavelength may exceed the thickness of the device, and in this case, the action of the terahertz electromagnetic wave can be considered as the one of a uniform time-dependent electric field acting on the TFR <NUM>, which may be considered an effective capacitor-device. Hence, the response of the TFR <NUM><NUM> can be described by the effective dynamic frequency-dependent impedance, ZTFR. In case of a a heterostructure formed by N pairs of ferroelectric layers <NUM> and N pairs of dielectric layers <NUM>, the effective dynamic frequency-dependent impedance ZTFR may be described as <MAT> where hd is the thickness of one of the dielectric layers <NUM>, εd is the dielectric constant of one of the dielectric layers <NUM>, hf is the thickness of one of the ferroelectric layers <NUM>, εf is the dielectric constant of one of the ferroelectric layers <NUM>, ε<NUM> is the dielectric permittivity of vacuum, and S is the lateral area of the heterostructure. The frequency-dependence of εf in the frequency range of the sub-THz to THz signal is related to the oscillations of the polarization pattern and the corresponding resonances. It may hence be controlled by controlling the resonances, for example by controlling the resonance frequencies and dynamical vibration modes and/or selecting a specific dynamical vibration mode, for example a principal and/or main resonance mode with a main and/or principal resonance frequency.

As an example, the effect of a resonance corresponding to a specific dynamical vibration mode related to an alternating shrinking-expanding oscillation of a domain chain on εf will be presented. For this example, εf = εf(ω) may be expressed in the following equation, which is derived in <NPL>): <MAT> where Γ is a damping factor, which is related to energy dissipation. For example, energy dissipation may be due to domain wall vibrations. A non-uniformity factor g~<NUM> - <NUM> accounts for non-uniformities of an electric field distribution near an interface between one of the dielectric layers <NUM> and one of the ferroelectric layers <NUM>.

<FIG> illustrates an exemplary dielectric constant <NUM> as a function of frequency v (THz) (where v (THz) = ω/2π) according to an embodiment of the disclosure. The dielectric constant has complex values, and in <FIG> the real part Re ε of the dielectric constant <NUM> and the imaginary part Im ε of the dielectric constant <NUM> are depicted separately. The resonance frequency v<NUM> = ω<NUM>/<NUM>π, may be read from the graph as the frequency at which the real part Re ε of the dielectric constant <NUM> is zero. The resonance frequency is advantageously located in the frequency range of the sub-THz to THz signal.

<FIG> shows a graph <NUM> illustrating the influence of the thickness hf of one of the ferroelectric layers on the resonance frequency vo (where v<NUM> = ω<NUM>/<NUM>π) according to an embodiment of the disclosure with a ferroelectric layer <NUM> composed of PbTiO<NUM> and a dielectric layer <NUM> composed of SrTiO<NUM>. The thickness hf of the ferroelectric layer may advantageously be selected to adjust the resonance frequency. For example, a predefined maximum thickness of an individual layer of the heterostructure or a predefined maximum thickness of any of the layers of the heterostructure may be adjusted, for example to a value of <NUM>, in particular <NUM> or <NUM>. By doing so, the resonance frequency can advantageously be matched to a frequency of the sub-THz to THz signal to achieve a strong and efficient coupling between the oscillation of the polarization pattern and the sub-THz to THz signal, for example by resonant coupling. In addition, a material of the ferroelectric layer <NUM> and a material of the dielectric layer <NUM> can advantageously be selected to adjust the resonance frequency v<NUM>. In addition, a static electric field and/or a mechanical stress can be applied to the heterostructure advantageously to adjust the resonance frequency vo.

<FIG> shows the dependence of the impedance amplitude |ZTFR|on the frequency v(THz). The graph <NUM> gives the impedance amplitude |ZTFR| for three different thicknesses of the ferroelectric layer, where h1 corresponds to hf = hd = <NUM>, h2 corresponds to hf = hd = <NUM>, and h3 corresponds to hf = hd = <NUM>. The impedance amplitude |ZTFR| has a maximum at a frequency similar or identical to the resonance frequency vo. The frequency-dependence of the impedance amplitude of the heterostructure is similar to the frequency-dependence of the impedance amplitude of well-known electronic components, like for example parallel LC resonant circuits. Hence, the heterostructure and the TFR <NUM> device may be employed in an electronic device like, for example, a signal receiver, a transmitter, or a processing device, operating in the frequency range of the sub-THz to THz signal, and the integration and application of the heterostructure and the TFR <NUM> device can advantageously make use of highly developed concepts for the integration and application of the well-known electronic components, like for example of the LC resonant circuit.

According to the disclosure, the thickness hf of the ferroelectric layer may advantageously be selected to adjust the resonance frequency vo and consequently the frequency-dependence of the impedance amplitude, in particular the frequency at which the impedance amplitude has a maximum. Again, also the material of the ferroelectric layer <NUM> and the material of the dielectric layer <NUM> can advantageously be selected, and/or a static electric field and/or a mechanical stress can be applied to the heterostructure to adjust the resonance frequency ω<NUM>.

<FIG> and <FIG> illustrate example applications, for which a signal receiver, transmitter, or processing device using a TFR <NUM> and operating in the frequency range of the sub-THz to THz signal may be particularly beneficial.

For example, as illustrated in <FIG>, a device employing a TFR <NUM> as a component of a transmitter and/or a receiver for a terahertz electromagnetic wave may find application in satellite communications. Terahertz electromagnetic waves <NUM> may be exchanged between a first satellite <NUM> and a second satellite <NUM>, each comprising a transmitter and/or a receiver based on a TFR <NUM>. The space between the satellites is transparent in the terahertz spectral range to permit the propagation of the terahertz electromagnetic waves <NUM>. The TFR <NUM> and in particular an integrated circuit with a TFR <NUM> may provide highly energy-efficient communication means for the first satellite <NUM> and the second satellite <NUM>, in an environment where energy efficiency is particularly important. The TFR <NUM> also provides lightweight communication means, which can reduce the cost of launching the first satellite <NUM> and the second satellite <NUM> into space. Importantly, resonant coupling between terahertz electromagnetic wave <NUM> and the TFR <NUM> provides frequency-selective communication means, suppressing noise from radiation at frequencies different from the resonance frequency of the TFR <NUM>. This advantage may be particularly important in a space environment, where radiation at various frequencies maybe abundant.

Moreover, as illustrated in <FIG>, a device employing a TFR <NUM> as a component of a transmitter and/or a receiver for a terahertz electromagnetic wave may form a basis for <NUM> WiFi communication <NUM> in this frequency range. The TFR <NUM> may be highly integrated with other electric components of an integrated electric circuit of a communication hub or an end user device <NUM>, thus providing a cost-efficient communication technology for consumer products. In particular, the same or similar TFRs <NUM> in a single device may be used for coupling to the electromagnetic wave <NUM> on the one hand, and for electronic signal processing within the integrated circuit on the other. Both the communication hub and the end user device <NUM> may comprise integrated circuits each with one or multiple TFRs <NUM>.

The TFR <NUM> device according to the disclosure is advantageously compatible with the integration into existing, miniaturized and highly developed semiconductor technology and integrated circuitry. Because of its small lateral area, the TFR <NUM> may be co-integrated with semiconductor devices such as diodes or transistors.

<FIG> illustrates an integrated circuit <NUM> with a TFR <NUM> and a semiconductor device <NUM> according to an embodiment of the disclosure. A portion of the TFR <NUM> device may be processed, for example deposited or structured, in a single process step together with a portion of the semiconductor device <NUM>. For example, a layer of the TFR <NUM>, such as a dielectric layer <NUM>, a ferroelectric layer <NUM>, or a bottom electrode <NUM> and/or a top electrode <NUM> of the TFR <NUM> device may be deposited together with a similar layer of the semiconductor device <NUM> in a single deposition step. Also, a layer of the TFR <NUM> device may be etched together with a layer of the semiconductor device in a single etching step. Also, a layer of the TFR <NUM> device may be masked together with a layer of the semiconductor device in a single masking step. A driver circuit to drive the transmitter for the terahertz electromagnetic wave or a readout circuit to read the receiver for the terahertz electromagnetic wave may be implemented making use of a semiconductor device <NUM> such as a diode or a transistor. For example, the heterostructure of the TFR <NUM> may be coupled to a diode or transistor <NUM>, in particular to a gate of a transistor, to implement a rectifier converting the sub-THz to THz signal of the terahertz electromagnetic wave from an oscillation into a polar signal.

Frequency-dependent properties of a TFR <NUM> device, in particular the frequency-dependence of the impedance amplitude of the TFR <NUM>, may advantageously be optimized for application in a specific device. In addition, the frequency-dependent impedance of a circuit comprising the TFR <NUM> device, like, for example, an RC circuit, may be optimized by integrating additional electric components, like a load resistor, in the circuit. A load resistor may either be implemented as a load resistor <NUM> integrated in series with the TFR <NUM> device as illustrated in <FIG>, or as a load resistor <NUM> integrated in parallel with the TFR as illustrated in <FIG>.

<FIG> and <FIG> show the corresponding circuit diagrams <NUM>, <NUM> with the electronic graphical symbol <NUM> of the TFR <NUM>, a resistor in series <NUM>, and a resistor in parallel <NUM>.

Implementing the circuit according to the circuit diagram <NUM> of <FIG> may be achieved by forming an extended top electrode <NUM> or an extended bottom electrode <NUM> integrating with an additional resistive part <NUM> composed of one or several, metallic or semiconducting layers, whose thickness and material composition may be selected to optimize the resistance according to the requirements of the application in a specific device.

Implementing the circuit according to the circuit diagram <NUM> of <FIG> may be achieved by integrating a parallel load as a shunt-like structure, with a metallic or semiconducting shunt <NUM> connecting the top electrode <NUM> and bottom electrode <NUM>. The metallic or semiconducting shunt <NUM> may be arranged between the top electrode <NUM> and bottom electrode <NUM>, or at least a portion of the metallic or semiconducting shunt <NUM> may be arranged outside the volume between the top electrode <NUM> and bottom electrode <NUM>.

<FIG> shows another example of an integrated circuit <NUM> comprising two TFRs <NUM>. Because of its small size, the TFR <NUM> can be co-integrated into a variety of integrated circuits. Additional examples of integrated circuits which may comprise and/or be based on the TFR <NUM> include a terahertz antenna, a transmitter and a receiver, which may also be referred to as a sensor of terahertz radiation. In particular, a device of an integrated circuit comprising the TFR <NUM> may be applied as a receiver to detect a sub-THz to THz signal emitted from another device of the integrated circuit.

Alternatively, or in addition, a device of an integrated circuit comprising the TFR <NUM> may be applied as a transmitter to generate a sub-THz to THz signal to be detected by another device of the integrated circuit. Advantageously, a transmitter based on the TFR <NUM> and a receiver based on the TFR <NUM> can be arranged on the same integrated circuit for the transmission, guiding, and/or manipulation of a sub-THz to THz signal. <FIG> shows an example of a corresponding integrated circuit <NUM>. In this example, the semiconductor devices <NUM> could, for example, correspond to a processor or a memory device. The TFR <NUM> may be used to establish a communication between the semiconductor devices <NUM> via a terahertz electromagnetic wave <NUM>. The terahertz electromagnetic wave <NUM> may be an electromagnetic wave propagating freely in vacuum, gas, a dielectric or another form of matter, or it may be guided by a waveguide structure or it may be supported by a metallic channel, in particular by a plasmonic channel. In this embodiment, the TFR <NUM> serves as a component of the integrated electric circuit, for example as a transmitter, receiver, or transceiver, but it may in addition serve as a terahertz optical device, which will be described in more detail later.

<FIG> shows a circuit diagram <NUM> corresponding to an embodiment of a frequency filter with a TFR <NUM>. A circuit according to the circuit diagram <NUM> may be employed as a low pass filter, a high pass filter, or a bandpass filter. The high pass filter may be implemented by placing an input voltage, Uin, across both the TFR <NUM>, <NUM> and the resistor in series <NUM> as depicted in <FIG>. The TFR <NUM>, <NUM> has an impedance ZTFR (ω). The resistor in series <NUM> has a resistance R, which is essentially independent of frequency. The high pass filter may be completed by using as an output voltage Uout,high a voltage across the resistor in series <NUM>. The output voltage Uout,high may be described using the equation: <MAT>.

<FIG> illustrates the frequency dependence of the output voltage Uout,high <NUM> of a high pass filter according to an embodiment of the disclosure.

A low-pass filter is realized by the same circuit where the voltage output, Uout,low, is taken from the TFR <NUM>. <FIG> illustrates the frequency-dependent output voltage Uout,low <NUM> for the low-pass filter, as given by <MAT>.

Making use of the coupling of the TFR <NUM> to a terahertz electromagnetic wave, the TFR <NUM> can also be employed in a terahertz optical device to guide the terahertz electromagnetic wave and/or manipulate its properties, like its amplitude, phase, direction, or (in case of pulsed terahertz electromagnetic radiation) pulse shape. Advantageously, due to the layered structure of the heterostructure of the TFR <NUM>, highly developed techniques for the design of layered dielectric optics can be used to tailor the TFR <NUM> to the requirements of a specific application, for example as a mirror, a beam splitter, an attenuator, a phase shifter, a dichroic mirror, a (terahertz) optical high pass filter, a (terahertz) optical low pass filter, a (terahertz) band pass filter, or a (terahertz) optical notch filter. Advantageously, the use of a device with the TFR <NUM> as a terahertz optical device may be combined with the use of the same device as an electronic resonator, for example as a receiver. In particular, a portion of the terahertz electromagnetic wave absorbed in the TFR <NUM> may be used for sensing, whereas another portion of the terahertz electromagnetic wave may be guided, reflected, or transmitted by the same TFR <NUM> serving as a terahertz optical device.

<FIG> shows an example of a terahertz optical device <NUM> with a TFR <NUM> to manipulate a terahertz electromagnetic wave according to an embodiment of the disclosure. The terahertz optical device <NUM> may reflect a portion of an incident terahertz electromagnetic wave <NUM> to generate a reflected terahertz electromagnetic wave <NUM>. The device may also transmit a portion of the incident terahertz electromagnetic wave <NUM> to generate a transmitted terahertz electromagnetic wave <NUM>. Moreover, the terahertz optical device <NUM> may absorb a portion of the incident terahertz electromagnetic wave <NUM>. The terahertz optical device <NUM> may use the portion of the incident terahertz electromagnetic wave <NUM> absorbed by the device for electronic signal processing, for example for sensing the incident terahertz electromagnetic wave <NUM>.

<FIG> illustrate the optical properties as a function of frequency v(THz) of a heterostructure according to an embodiment of the disclosure. <FIG> shows the complex refractive index <MAT><NUM>. Since the complex refractive index <NUM> is a complex quantity, the real part Re n of the complex refractive index <NUM> and the imaginary part Im n of the complex refractive index <NUM> are given separately. <FIG> gives the corresponding terahertz optical reflection coefficient Ro for normal incidence. The terahertz optical reflection coefficient Ro may be related to the complex refractive index <MAT><NUM> as: <MAT>.

Properties of the layers of the heterostructure of the TFR <NUM>, like the dielectric layers <NUM>, the ferroelectric layers <NUM>, the bottom electrode <NUM> and the top electrode <NUM> may be adjusted using the highly developed techniques for the design of layered dielectric optics. In particular, the properties of the layers of the heterostructure can be adjusted to achieve a desired amplitude, phase, or direction of the reflected terahertz electromagnetic wave <NUM> and/or of the transmitted terahertz electromagnetic wave <NUM>. For example, the thicknesses and the material compositions of the layers of the heterostructure may be adjusted. Alternatively or in addition, a static electric field and/or a mechanical stress can be applied to the heterostructure, constantly or dynamically (e. g for terahertz optical switching), to adjust the resonance frequency ω<NUM>. The terahertz optical device with a TFR <NUM> may, for example, advantageously be applied in wireless terahertz communication technologies or for on-chip wireless signal transmittance and processing. In some of these applications, it may be useful to adjust the thickness of the heterostructure to exceed or be comparable with the radiation wavelength. This may complicate the deposition of a bottom electrode <NUM> or a top electrode <NUM>. Advantageously, in application where the terahertz optical device <NUM> is not used for electronic signal processing, the deposition of a top electrode <NUM> and/or a bottom electrode <NUM> may be omitted.

Claim 1:
A method of employing a device (<NUM>) as a resonator for electrons of an electrical circuit (<NUM>, <NUM>, <NUM>, <NUM>) or for a terahertz electromagnetic wave (<NUM>, <NUM>, <NUM>, <NUM>), the device comprising:
a heterostructure (<NUM>, <NUM>);
a bottom electrode (<NUM>) arranged below the heterostructure (<NUM>, <NUM>); and
a top electrode (<NUM>) arranged above the heterostructure (<NUM>, <NUM>);
wherein:
the heterostructure (<NUM>, <NUM>) comprises a plurality of dielectric layers (<NUM>), a plurality of ferroelectric layers (<NUM>), and an alternating stacking sequence of the dielectric layers of the plurality of dielectric layers (<NUM>) and the ferroelectric layers of the plurality of ferroelectric layers (<NUM>), wherein: the ferroelectric layers (<NUM>) comprise respective pluralities of ferroelectric polarization domains (<NUM>, <NUM>) forming respective polarization patterns, and the polarization patterns are adapted to execute respective oscillations with resonance frequencies in a terahertz frequency range;
wherein the method comprises:
functionally coupling the oscillations of the polarization pattern and an oscillation of the electrons of the electrical circuit (<NUM>, <NUM>, <NUM>, <NUM>) or of the terahertz electromagnetic wave (<NUM>, <NUM>, <NUM>, <NUM>) by the device (<NUM>).