This disclosure describes a system and method for nonplanar nanostructure fabrication by controlled delamination through surface engineering.
Nonplanar nanostructures, which are made up of suspended ultrathin films and nanogaps, are required for next generation miniaturized nanoelectromechanical systems (NEMS), photonic elements, metamaterials and other devices. However, these structures suffer from instabilities that are caused by van der Waals and capillary forces, which become increasingly dominant at the nanoscale. These forces may make it difficult to perform nonplanar fabrication through conventional top-down techniques, which often require the application and subsequent removal of a sacrificial support layer. The instabilities involved in this process become more prominent as dimensions reduce to the few-nanometers regime, resulting in low process yield. Smaller device sizes are needed for improved device efficiency, speed, sensitivity, and the creation of new functionality.
Various techniques are currently used to fabricate these three-dimensional nanostructures beyond the conventional sacrificial layer approach. These include additive manufacturing using electron- and ion-beam induced processes, two-photon lithography, and kirigami. However, each of these approaches is typically limited to features that are greater than 100 nm. These structures are often not mechanically-active, and are largely incompatible with conventional wafer-scale processes.
Thus, it would be beneficial to overcome the inherent limits of top-down strategies to allow the development of nonplanar designs at small dimensions. Further, it would be advantageous if the system and method allows nanostructures of different dimensions to be predictably fabricated with spatial control.
A method of forming nonplanar nanostructures on a substrate is disclosed. The method includes treating a portion of the surface of the substrate so as to affect its properties. A film is then applied to the substrate after the surface engineering has been completed. Energy is then applied to the film, causing it to delaminate in the regions where the surface was treated, thereby creating the nonplanar nanostructures. The surface treatment may include the application of a self-assembled molecular (SAM) layer, which includes an anchoring group that allows assembly on the surface of the substrate, and also has a functional group that has the desired interaction with the film. The nonplanar nanostructures may be used to form nanoswitches, resonators, sensors, actuators, active matter, and strain engineered surfaces. There are also other applications of these nonplanar nanostructures.
According to one embodiment, a method of surface engineering is disclosed. The method comprises treating a portion of a surface of a substrate to produce an engineered surface; applying a film over the engineered surface; and applying energy to induce delamination of the film from the engineered surface so as to form a nonplanar nanostructure. In some embodiments, the substrate comprises silicon. In some embodiments, the substrate comprises an oxide, a nitride or a metallic material. In some embodiments, treating a portion of the surface comprises applying a self-assembled molecular (SAM) layer to the portion of the surface. In some embodiments, treating a portion of the surface comprises applying a patterned mask to the surface; depositing a self-assembled molecular (SAM) layer to the surface after application of the patterned mask; and removing the patterned mask after depositing the SAM layer. In some embodiments, the SAM layer comprises (3-Aminopropyl)triethoxysilane (APTES). In some embodiments, the molecules in the SAM layer have an anchoring group and a functional group; and the anchoring group is a silane group, an OH group, an COOH group or a thiol group and the functional group is an amine group, a hydroxyl group or a carboxyl group. In some embodiments, the film comprises an oxide. In certain embodiments, the film comprises Al2O3 or HfO2. In some embodiments, the film has a thickness of between 2 and 40 nm. In some embodiments, the film is applied using atomic layer deposition. In some embodiments, the applied energy is light, heat or an electron beam. In some embodiments, the nonplanar nanostructure is a dome shaped nanostructure, and the method further comprising applying a second mask to portions of the dome shaped nanostructure; and removing the film in exposed regions so as to form a bridge structure.
In some embodiments, the film comprises a plurality of layers. In certain embodiments, one of the plurality of layers comprises a metal layer. In certain embodiments, the metal layer is a partial layer. In some embodiments, a first layer comprises an oxide and a second layer, disposed on the first layer, comprises a two-dimensional material. In certain embodiments, the second layer is conformally adhered to the first layer. In some embodiments, the delamination induces strain in the two-dimensional material. In some embodiments, the strain changes optical and/or electrical properties of the two-dimensional material. In some embodiments, the method further comprises applying an external stimulus to the nonplanar nanostructure to reduce or tune the strain. In some embodiments, the external stimulus is actively modulated. In some embodiments, the external stimulus is electrostatic, mechanical, thermal, or piezoelectric.
According to another embodiment, a resonator is disclosed. The resonator comprises a film formed in a bridge structure, having two ends that contact the substrate and a middle portion suspended above the substrate by a gap; wherein the gap is between 5 nm and 5 um. In some embodiments, the film comprises an Al2O3 or HfO2. In some embodiments, the film comprises a plurality of layers. In certain embodiments, a first layer comprises an oxide layer. In certain embodiments, a second layer comprises a metal. In certain embodiments, a second layer is a partial layer that does not cover an entirety of a first layer. In some embodiments, a metal layer is disposed on the substrate beneath the gap.
According to another embodiment, an electronic device is disclosed, wherein the electronic device comprises a nonplanar nanostructure formed using the method described above.
According to another embodiment, a nonplanar nanostructure is disclosed. The nonplanar nanostructure is formed on a substrate and comprises a film in a form of a dome shaped blister, wherein a middle portion of the blister is suspended above the substrate by a gap; wherein the gap is between 5 nm and 5 μm. In some embodiments, the film comprises an Al2O3 or HfO2. In some embodiments, the film comprises a plurality of layers. In certain embodiments, a first layer comprises an oxide layer. In certain embodiments, a second layer comprises a metal. In certain embodiments, a second layer is a partial layer that does not cover an entirety of a first layer. In some embodiments, a metal layer is disposed on the substrate beneath the gap. In some embodiments, a second layer comprises a two dimensional material. In certain embodiments, the two dimensional material is a transition metal dichalcogenide.
For a better understanding of the present disclosure, reference is made to the accompanying drawings, in which like elements are referenced with like numerals, and in which:
The present disclosure describes an approach in which nonplanar nanostructures may be fabricated using planar processes enhanced with surface engineering, which may be used to deterministically induce controlled, selective delamination of two adjacent surfaces.
First, as shown in
In one particular embodiment, the mask 20 is a Al2O3 hard mask that is patterned using a positive photoresist. In this embodiment, a Al2O3 layer is created using atomic layer deposition (ALD), which is used to create an Al2O3 layer having a thickness of 1-5 nm. After, a positive photoresist may be lithographically patterned on top of the Al2O3 layer and developed using tetramethylammonium hydroxide (TMAH) developer. During development, the exposed Al2O3 layer is also etched by the TMAH developer, thereby allowing the Al2O3 to be patterned as well. The photoresist may then be removed using acetone, leaving the patterned Al2O3 hard mask. This technique may be beneficial in that the photoresist is never in contact with the surface 11 of the substrate 10. In some embodiments, the patterns may comprise one or more circles or squares. While this embodiment describes a hard mask made using a positive photoresist, other embodiments are also possible. For example, the hard mask may utilize a negative photoresist material. In another embodiment, the mask may be constructed using an electron-beam resist rather than a photoresist.
Next, the surface 11 of the substrate 10 is treated to form an engineered surface. In one embodiment, shown in
After the SAM layer 30 has been assembled, the mask 20 is removed, as shown in
Next, as shown in
Next, an external stimulus, in the form of an applied energy, is used to create the nonplanar nanostructures 50, as shown in
In certain embodiments, the SAM regions are circular, such that the nonplanar nanostructures resemble blisters, each having a dome shape. These blisters may range in diameter from 50 nm to tens of microns, depending on the dimension of the SAM regions.
While
Thus, by applying surface engineering to a portion of the surface 11 of a substrate 10, a nonplanar nanostructure 50 may be created. The surface engineering comprises applying a surface modification to a portion of the surface 11 of the substrate 10. This surface modification may provide a low-adhesion property to the surface 11 of the substrate 10, facilitating the delamination of the film 40 during the energy application process. Thus, the surface engineering facilitates deterministically induced controlled delamination of two adjacent surfaces.
The process described above may be customized to achieve varying dimensions of the nonplanar nanostructure 50. The terms “nonplanar nanostructure” and “blister” are used interchangeably herein. For example, the dimensions of the area of the surface 11 on which the SAM layer is directly applied may help determine the final size of the nonplanar nanostructure.
Alternatively or additionally, the dimensions of the nonplanar nanostructure 50 may be tuned by varying the thickness of the film 40 and the temperature used to induce the delamination. Specifically, in some embodiments, thicker films may result in larger nonplanar nanostructures forming more readily at lower temperatures. Conversely, thinner films require higher temperatures to form nonplanar nanostructures, and the resulting nanostructures may be smaller. The dependence of blister diameter on film thickness, based on the results of one experiment, is demonstrated in
While the previous disclosure and figures show nanostructures that are in the shape of dome shaped blisters, other embodiments are also possible. For example, in one embodiment, after the process shown in
A simulation of the bridge structure shown in
As noted above, the film 40 may include a plurality of layers.
For example, conductive layers may be included above and/or below the nanostructure to act as electrodes, enabling the electrostatic actuation of the structure In
Some applications may require separate top and bottom electrodes for each device to make them individually addressable. In this case, conductive layers may be patterned both above and below the nanostructure. In
The process shown in
In this embodiment, one or a plurality of nonplanar nanostructures may be created on the substrate 10 to create a textured surface 43, imparting altered optical or electronic properties to the textured surface 43 by varying the strain present in second layer 42.
Experiments were performed using different transition metal dichalcogenide two-dimensional materials. First, the processes shown in
Raman spectroscopy was also used to validate the strain demonstrated in
In a second set of experiments, the second layer 42 was WSe2.
The process described in
Additionally, the design of the nanostructures may be defined before and/or after they are formed through further processing, for instance, through lithographic steps, such that topographies other than domes may be implemented. Additionally, the strained nanostructures formed may also be mechanically active in response to various external stimuli including electrostatic, mechanical, thermal, and piezoelectric, and others. This electromechanical feature allows for dynamic and reversible tuning of the strain, such that the intrinsic properties of the materials of interest may be actively modulated. If integrated with a closed-loop feedback system, this may further allow for deterministic fine-tuning of properties to achieve the desired functionalities. The strain engineering described herein allows diverse applications including in electronic devices (such as transistors) with improved mobilities, single photon sources that can be dynamically tuned, lasers, strain/pressure/mass sensors or other sensors, high-resolution nanoimaging, optical lenses, solar energy funnels, and optical and mechanical resonators.
While
The present system and method have many advantages. The disclosed method enables novel opportunities for the fabrication of three-dimensional structures, nanogaps, and mechanically-active designs leading to diverse applications in optics, photonics, nanoelectronics, and electromechanical systems. Applications are diverse with significant impact, including in the development of optical and mechanical resonators, meta-surfaces, sensors, vacuum electronics, electromechanical switches, sensors and actuators. The present method may also provide an approach for structural texturing of nanomaterials and thin-films including two-dimensional layered materials to achieve strain engineering or other effects, as shown in
A particular impact of the present method is in the development of technologies that require nanoscale gaps and mechanically-active structures. An example is in the field of micro/nanoelectromechanical systems (MEMS/NEMS) which has formed a multi-billion-dollar industry by developing diverse technologies including gyroscopes, accelerometers, and various types of sensors, switches, and actuators. To expand the prospects of this field, a foundational goal has been to improve the stability of electromechanical devices while also enabling their miniaturization. This is a fundamental challenge for conventional fabrication techniques, as the inevitable surface adhesive forces cause instability and even structural collapse. The present method addresses this challenge to develop much-desired, yet conventionally inaccessible, devices and systems for a multitude of emerging applications. As an example,
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are intended to fall within the scope of the present disclosure. Further, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.
This application claims priority to U.S. Provisional Patent Application Ser. No. 63/323,372, filed Mar. 24, 2022 and U.S. Provisional Patent Application Ser. No. 63/374,737, filed Sep. 6, 2022, the disclosures of which are incorporated by reference in their entireties.
Filing Document | Filing Date | Country | Kind |
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PCT/US2023/016143 | 3/23/2023 | WO |
Number | Date | Country | |
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63323372 | Mar 2022 | US | |
63347737 | Jun 2022 | US |