Patent Application
20240332794
Reconfigurable intelligent surfaces are specifically designed manmade surfaces of electromagnetic material, referred to as metamaterial, that are electronically controlled with integrated electronics. Metamaterials are artificially engineered materials fabricated using a stack of metal and dielectric layers. These thin two-dimensional metasurfaces can tune an electromagnetic wave's key properties, such as amplitude, phase, and polarization, as the electromagnetic wave is reflected or refracted by the surface. In other words, a reconfigurable intelligent surface is a two-dimensional surface whose surface can be electronically altered such that it changes the characteristics of any incoming electromagnetic wave, including the wave's phase.
Each metasurface typically is made up of (possibly up to) hundreds or thousands of unit-cells, and because the individual unit-cell can be controlled, reconfigurable intelligent surfaces can provide programmable and smart wireless environments. For example, one scenario is to use such a surface to intelligently reconfigure wireless communications. More particularly, objects in the path of a wireless signal, such as buildings and trees, can block wireless communication signals at higher frequencies, including millimeter-wave frequency bands (24.5 gigahertz, or GHz-52.6 GHZ), and even higher frequencies such as the U-Band (40-60 GHz) and the V-Band (60-75 GHZ), which are expected to move upwards to sub-terahertz bands. This can be overcome by installing a large number of base stations to provide coverage to otherwise blocked areas, but doing so would increase the infrastructure costs many times. Instead, a relatively inexpensive metasurface can be installed at various locations to reflect and/or refract higher frequency signals to otherwise blocked or weak coverage areas.
Various ways to control reconfigurable intelligent surfaces have been implemented, including those based on switching technologies such as field-effect transistors (FETs) and PIN diodes (formed from a p-type semiconductor, an undoped intrinsic region and an n-type semiconductor). With such switches used in each unit cell, the wireless operating frequency is a major factor because each of these existing switch technologies has different maximum operating frequencies and other frequency-dependent characteristics. For wireless communications beyond fifth generation (5G), such as 6G's sub-terahertz bands and even future terahertz bands, switch technologies like PIN diodes and FETs are not suitable. Further, with these technologies, switch size factors, ON-state series resistance, and overall power consumption (e.g., PIN diodes require continuous power when in an ON state, and there can be hundreds or thousands of unit cells) are also significant drawbacks.
The technology described herein is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which:
Various aspects of the technology described herein are generally directed towards a phase change material-based device that can be used in a unit cell of a reconfigurable intelligent surface. In general and as will be understood, the phase change material can be configured to have different widths of conductive portions relative to non-conductive portions. The relative widths determine the phase shift of a unit cell that includes the device.
As a result, control of the reconfigurable intelligent surface with respect to redirecting an impinging an electromagnetic wave is achieved by varying the relative widths in relevant unit cells, and therefore controlling the phase shift of each unit cell. A controller or the like controls the conductive or resistive states over different areas of the phase change material to achieve desired redirection.
It should be understood that any of the examples herein are non-limiting. As one example, a unit cell of a reconfigurable intelligent surface is described that is based on switching elements made of chalcogenide materials, e.g., alloys based on germanium-antimony-tellurium (GeSbTe); however this is only one non-limiting example, and other materials, including those not yet developed, can be leveraged by the technology described herein. Thus, any of the embodiments, aspects, concepts, structures, functionalities or examples described herein are non-limiting, and the technology may be used in various ways that provide benefits and advantages in communications and computing in general. It also should be noted that terms used herein, such as “optimize” or “optimal” and the like only represent objectives to move towards a more optimal state, rather than necessarily obtaining ideal results.
Reference throughout this specification to “one embodiment,” “an embodiment,” “one implementation,” “an implementation,” etc. means that a particular feature, structure, or characteristic described in connection with the embodiment/implementation can be included in at least one embodiment/implementation. Thus, the appearances of such a phrase “in one embodiment,” “in an implementation,” etc. in various places throughout this specification are not necessarily all referring to the same embodiment/implementation. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments/implementations. Repetitive description of like elements employed in respective embodiments may be omitted for sake of brevity.
The following detailed description is merely illustrative and is not intended to limit embodiments and/or application or uses of embodiments. Furthermore, there is no intention to be bound by any expressed or implied information presented in the preceding sections, or in the Detailed Description section.
One or more embodiments are now described with reference to the drawings, wherein like referenced numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a more thorough understanding of the one or more embodiments. It is evident, however, in various cases, that the one or more embodiments can be practiced without these specific details.
Further, it is to be understood that the present disclosure will be described in terms of a given illustrative architecture; however, other architectures, structures, substrate materials and process features, and steps can be varied within the scope of the present disclosure.
It will also be understood that when an element such as a layer, region or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, only if and when an element is referred to as being “directly on” or “directly over” another element, are there are no intervening element(s) present. Note that orientation is generally relative; e.g., “on” or “over” can be flipped, and if so, can be considered unchanged, even if technically appearing to be under or below/beneath when represented in a flipped orientation. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, only if and when an element is referred to as being “directly connected” or “directly coupled” to another element, are there no intervening element(s) present.
Aspects of the subject disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which example components, graphs and/or operations are shown. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. However, the subject disclosure may be embodied in many different forms and should not be construed as limited to the examples set forth herein.
The control/bias network 110 for the heaters is designed on fifth layer, followed by a dielectric layer 112, which is coated on a high permittivity substrate 114. The bottom of the substrate is coated by another thin metallization layer 116. The heating elements can be individually controlled as described herein.
Chalcogenide material is formed with alloys containing group VI elements such as sulfur (S), selenium (Se) and telluride (Te). Among these, the alloys formed from different ratio combinations of germanium, antimony, and telluride (Ge—Sb—Te, or GST alloys) are currently the most popular for radio frequency and optical memory applications. In general, single-phase alloys are made of germanium telluride (GeTe) and antimony telluride (Sb2Te3). Alloys include GelSb2Te4, Ge2Sb2Te5, and GelSb4Te7. Depending on the alloy used, the properties range from high stability and low speed to low stability and high speed. The GST alloys have a unique property of reversibly switching between amorphous and crystalline states upon specific heat treatment by means of electrical pulses, hence the name “phase-change.” The state in which atoms are arranged in a disorderly manner (short range order) is called the amorphous state, whereas the state where atoms are organized in an orderly manner (long range order) is called crystalline state. The disordered amorphous state has a lower mean free path of conduction for electrons that impedes current flow due to electron scattering, thus resulting in a higher resistance when compared to the crystalline state.
The operation principle of the example unit cell structure 100 of
Turning to tuning the unit cells' individual phases, in one example implementation the respective unit cells can be based on the effective operational width of the respective chalcogenide elements such as described in the examples herein. As shown in
It should be noted that the heating elements of the heater network 106 can be, but need not be, symmetrical or substantially symmetrical with respect to their separation distances. Further, the heating elements can be, but need not be, the same widths or substantially the same widths, nor need they necessarily be parallel or substantially parallel to one another.
The device performance can be simulated using full-wave 3D electromagnetic (EM) simulation software, and the phase shift offered to the reflected signal can be evaluated for a discrete set of widths, which can be electronically controlled. One example unit-cell was designed for operation around 50 GHZ, with an extremely large 27 GHz bandwidth. The relative phase shift offered to the reflected signal from the unit-cell is graphically represented in
A reconfigurable intelligent surface can be formed by arranging multiple unit cells in a two-dimensional m×n array, e.g., as shown in the surface 880 of
Thus, as shown in
Unlike other reconfigurable intelligent surfaces (in which each unit cell typically can only provide either a phase response of 0° or 180°; the coding for such a 1-bit digital cell state will be either “0” or “1” for OFF and ON switching, respectively), the analog-like reconfigurable intelligent surface described herein can use higher bit coding to describe the phase responses from individual unit cells. Depending on the beam steering precision desired by a given application, a system can select the number of phase states needed. For example, a 1-bit system with a single heating element can provide two possible phase states (chalcogenide switches can be used), while as described above, a system with more bits corresponding to more heating elements can provide more possible widths (e.g., the tunable chalcogenide unit cell as described herein) from each cell.
The technology described herein can function with a minimal power supply, as the electrical pulse is needed only during a change of configuration, a significant advantage over technologies that need continuous power to hold one of the states. Another significant and beneficial feature of this design is that the unit cells described herein can receive and transmit electromagnetic waves simultaneously, hence achieving full-duplex operation.
The technology described herein is suitable for reconfigurable intelligent surface-assisted wireless communications. Because the direct path between the access point and a target of interest can be fully/partially obstructed by other objects, the use of a reconfigurable intelligent surface can substantially improve the wireless network performance, particularly in crowded indoor/outdoor scenarios.
For example, with respect to an outdoor scenario, by installing the reconfigurable intelligent surface on common surfaces such as building walls, windows, billboards, traffic signs and the like, and because as described herein the direction of the reflected and/or refracted beams can be controlled, including remotely controlled, reasonably optimal reconfigurable intelligent surface deployment positions can be identified, along with the corresponding size of the reconfigurable intelligent surface needed. Reconfigurable intelligent surface placement and size can be in conjunction with the planning for a base station's position, or done afterwards by identifying the blind areas of poor signal strength in the network coverage map. This can not only improve the signal reception in the shadow areas, but also improve the data rates in the areas with an already good signal reception. Thus, a reconfigurable intelligent surface can be used for solving the network coverage problem of 5G/6G and even beyond, without adding much power/cost overhead.
Consider by way of example a typical scenario of an outdoor urban area with a single base station. For low frequency radio transmissions, the signal can propagate to long and far distances without significant attenuation due to its long wavelength. But high frequency signals suffer serious attenuation and blockage from objects, whereby the wireless coverage from a single base station will be weak, or even provide no coverage in certain zones. Depending on the location of the base station and the positions of the users, the (mostly) optimal location and size for reconfigurable intelligent surface on billboards, highway signs, walls, windows, and corners of the buildings can be selected.
The signals from the base station reflect off of (or can be refracted by) the passive reconfigurable intelligent surface, can be steered in the direction of most users, and also can be steered to other reconfigurable intelligent surface in the area for further reflection/refraction. The users close to the base station generally receive a direct path signal from the base station, and (likely) also receive a reflected signal from a reconfigurable intelligent surface. The users further away from the base station (or behind obstructions) can receive the reflected or refracted signals from one or multiple reconfigurable intelligent surfaces. One or more of the reconfigurable intelligent surfaces also can employ amplification to boost signals if and when appropriate.
In an indoor scenario, windows and walls can be covered with reconfigurable intelligent surface films, which can be generally transparent, in order to extend wireless coverage indoors. By locating such films on the windows, the signals coming from the outside can be refracted and boosted inside the building, enhancing the coverage inside. The signals to an illegitimate user, e.g., an eavesdropper, can be blocked by destructive interference.
One or more implementations can be embodied in a device, including a phase change material, and a controllable energy transfer component comprising a controllable heater network that selectively transfers heat to different individual portions of the phase change material to change an operational width of the phase change material with respect to redirecting an electromagnetic wave via a phase shift that is based on the operational width. The heater network is controlled to output heat via energy pulses to selectively change a first group of one or more of the different individual portions of the phase change material to a lower resistance state, and selectively change a second group of the one or more of the different individual portions of the phase change material to a higher resistance state, wherein the first group is different from the second group.
The first group can be within a first contiguous area of the phase change material bounded by a first subgroup of the second group in a second area of the phase change material, and bounded by a second subgroup of the second group in a third area of the phase change material that can be discontiguous from the second area. The first group can be substantially centered between the first subgroup and the second subgroup.
The second group can be within a first contiguous area of the phase change material bounded by a first subgroup of the first group in a second area of the phase change material, and bounded by a second subgroup of the first group in a third area of the phase change material that can be discontiguous from the second area. The second group can be substantially centered between the first subgroup and the second subgroup.
The first group can include at least two portions in discontiguous areas of the phase change material, and the second group can include subgroups that separate the discontiguous areas.
The phase change material and the controllable energy transfer component can be part of a unit cell of a reconfigurable intelligent surface.
The device can be coupled to a controller that controls individual heating elements of the controllable heater network to selectively output heat via an energy pulse to a selected heating element of the individual heating elements at a location corresponding to one area of the phase change material.
The phase change material can include at least one of: germanium telluride or antimony telluride.
One or more example aspects, such as corresponding to example operations of a method, are represented in
The phase shift can be a first phase shift, the target location can be a first target location, and further operations can include obtaining, by the system, information representative of a second target location, and, in response to the obtaining of the information, redirecting, by the system, the electromagnetic wave to the second location, which can include controlling the elements of the heater network to increase the low resistance area to enlarge the width of a conductive patch within the phase change material, the width of the conductive patch corresponding to a second phase shift.
The phase shift can be a first phase shift, the target location can be a first target location, and further operations can include obtaining, by the system, information representative of a second target location, and, in response to the obtaining of the information, redirecting, by the system, the electromagnetic wave to the second location, which can include controlling the elements of the heater network to decrease the low resistance area to reduce the width of a conductive patch within the phase change material, the width of the conductive patch corresponding to a second phase shift.
Controlling of the individual elements of the heater network to selectively output the heat can include pulsing a selected element with a voltage or current pulse to set a portion of the higher resistance area to a lower resistance portion, the lower resistance portion corresponding to a location of the selected element.
One or more implementations can be embodied in a unit cell, comprising a phase change material distributed over an area that corresponds to a surface of the unit cell, and a heater network including individually controllable heating elements distributed over the area to transfer heat to different portions of the phase change material. The individually controllable heating elements can be controlled to output heat corresponding to energy pulses to the different portions to change an operational width of the phase change material that is based on a higher resistance width corresponding to a higher resistance state of the phase change material, and a lower resistance width corresponding to a lower resistance state of the phase change material, in which the operational width determines a phase shift of the unit cell that redirects an electromagnetic wave impinging on the unit cell to a target location.
The unit cell can be a first unit cell of a reconfigurable intelligent surface including the first unit cell and a second unit cell, and the individually controllable heating elements of the first unit cell can be controlled to change the operational width of the phase change material to create constructive interference with the electromagnetic wave as redirected from the second unit cell.
The unit cell can be a first unit cell of a reconfigurable intelligent surface comprising the first unit cell and a second unit cell, and the individually controllable heating elements of the first unit cell can be controlled to change the operational width of the phase change material to create destructive interference with the electromagnetic wave as redirected from the second unit cell.
The unit cell can include a thermally conductive layer between the phase change material and the heater network.
The unit cell can include a thermal insulator layer and a dielectric layer, and wherein the thermal insulator layer is positioned between the heater network and a dielectric layer of the unit cell.
The phase change material in the lower resistance state and the dielectric layer can form a capacitor having a capacitance value determined by the operational width of the phase change material in the lower resistance state.
The electromagnetic wave can be between forty gigahertz and seventy-five gigahertz, inclusive.
As can be seen, there is described herein tunable devices with respect to their phase shifts, including for unit cells, and a highly reconfigurable intelligent surface design, in which programming the actuation voltage to the chalcogenide elements realizes different effective operational widths, which leads to changes in the phases of a reflected electromagnetic wave. Analog-like fine tuning can be achieved by controlling the actuation states per heating element, whereby the phase precision comes without increasing the complexity of the design. The reconfigurable intelligent surface described herein can operate at high frequencies such as U-Band and at least some V-Band frequencies. Chalcogenide-based radio frequency switches and tuning elements demonstrate suitable performance at such frequencies.
Moreover, the compact size of the chalcogenide element makes it highly suitable for monolithic integration with a wide range of technologies. Each chalcogenide switch can be implemented with a compact footprint in sub-micron sizes, including for shrinking reconfigurable intelligent surface cell size at higher frequencies, in which chalcogenide capacitive elements/switches fit more than adequately and can be monolithically integrated within each unit cell.
Still further, the reconfigurable intelligent surface offers low ON-state insertion loss; because some of the chalcogenide materials including germanium telluride has very low crystalline state (ON state) resistance of less than one Ohm, and low OFF-state capacitance of 7 fF (femto-farad), the figure of merit of the switches is 0.04 ps (picoseconds), which is far higher than any known commercially available PIN diodes or semiconductor RF switches.
The reconfigurable intelligent surface design and tunable capacitive element technology described herein needs power only during a state transition, thus saving significant power when in a steady state. Indeed, the chalcogenide material (especially germanium telluride) only needs an electrical pulse when transitioning from one state to another, as the material subsequently latches into a state. Hence, chalcogenide material does not need a continuous supply of power, which makes the design described herein suitable for implementing reconfigurable intelligent surfaces that can benefit from low power for operation.
What has been described above include mere examples. It is, of course, not possible to describe every conceivable combination of components, materials or the like for purposes of describing this disclosure, but one of ordinary skill in the art can recognize that many further combinations and permutations of this disclosure are possible. Furthermore, to the extent that the terms “includes,” “has,” “possesses,” and the like are used in the detailed description, claims, appendices and drawings such terms are intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.
The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
