Tag: materials science

C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications

In the search for lead-free, Si-microfabrication-compatible piezoelectric materials, thin films of scandium-doped aluminum nitride (Al,Sc)N are of great interest for use in actuators, energy harvesting, and micro-electromechanical-systems (MEMS).*

While the piezoelectric response of AlN increases upon doping with Sc, difficulties are encountered during film preparation because, as bulk solids with completely different structures and large differences in cation radii, ScN (rock salt, cubic) and AlN (wurtzite, hexagonal) are immiscible. *

Consequently, (Al,Sc)N is inherently thermodynamically unstable and prone to phase segregation. Film preparation is further complicated by the technological requirement for polar [001] or [00 1̲] out-of-plane texture, which is achieved using a seeding layer.*

In the article “C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications” Asaf Cohen, Hagai Cohen, Sidney R. Cohen, Sergey Khodorov, Yishay Feldman, Anna Kossoy, Ifat Kaplan-Ashiri, Anatoly Frenkel, Ellen Wachtel, Igor Lubomirsky and David Ehre propose a protocol for successfully depositing [001] textured, 2–3 µm thick films of Al0.75Sc0.25N.*

The procedure relies on the fact that sputtered Ti is [001]-textured α-phase (hcp). Diffusion of nitrogen ions into the α-Ti film during reactive sputtering of Al0.75,Sc0.25N likely forms a [111]-oriented TiN intermediate layer. The lattice mismatch of this very thin film with Al0.75Sc0.25N is ~3.7%, providing excellent conditions for epitaxial growth. In contrast to earlier reports, the Al0.75Sc0.25N films prepared in the current study are Al-terminated. Low growth stress (<100 MPa) allows films up to 3 µm thick to be deposited without loss of orientation or decrease in piezoelectric coefficient. *

An advantage of the proposed technique is that it is compatible with a variety of substrates commonly used for actuators or MEMS, as demonstrated here for both Si wafers and D263 borosilicate glass. Additionally, thicker films can potentially lead to increased piezoelectric stress/strain by supporting application of higher voltage, but without increase in the magnitude of the electric field. *

SEM, AFM, EDS, XRD and XPS techniques were used for the film characterization. For the nanoscale topography maps with atomic force microscopy (AFM) NanoWorld Pyrex-Nitride series PNP-TRS silicon nitride AFM probes were used in peak-force tapping1® mode. *

Figure 3 from Asaf Cohen et al. “C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications”: AFM images of (a) a (100) silicon wafer following cleaning procedures as described in the Materials and Methods section; (b) 50 nm-thick Ti film deposited on the wafer at 300 K; (c) the same film following exposure to N2 plasma at 673 K for 30 min. For the nanoscale topography maps with atomic force microscopy (AFM) NanoWorld Pyrex-Nitride PNP-TRS AFM probes were used in peak-force tapping mode1. *
Figure 3 from Asaf Cohen et al. “C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications”: AFM images of (a) a (100) silicon wafer following cleaning procedures as described in the Materials and Methods section; (b) 50 nm-thick Ti film deposited on the wafer at 300 K; (c) the same film following exposure to N2 plasma at 673 K for 30 min.

*Asaf Cohen, Hagai Cohen, Sidney R. Cohen, Sergey Khodorov, Yishay Feldman, Anna Kossoy, Ifat Kaplan-Ashiri, Anatoly Frenkel, Ellen Wachtel, Igor Lubomirsky and David Ehre
C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications
Sensors 2022, 22, 7041
DOI: https://doi.org/10.3390/s22187041

The article “C-Axis Textured, 2–3 μm Thick Al0.75Sc0.25N Films Grown on Chemically Formed TiN/Ti Seeding Layers for MEMS Applications” by Asaf Cohen, Hagai Cohen, Sidney R. Cohen, Sergey Khodorov, Yishay Feldman, Anna Kossoy, Ifat Kaplan-Ashiri, Anatoly Frenkel, Ellen Wachtel, Igor Lubomirsky and David Ehre is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third-party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.

1Peak Force Tapping® is a registered trademark of Bruker Corporation.

Happy Thanksgiving

Happy Thanksgiving to all our friends in the USA and Canada!

Enjoy the time with family and friends and don’t forget to visit us @NanoAndMore USA booth no. 311 @Materials_MRS MRS Fall 2022 after the holidays if you are planning to travel to Boston to participate in the conference. We’re looking forward to seeing you there.

 

Cartoon showing the NanoWorld professor and robot celebrating thanksgiving with a turkey in their lab
The NanoWorld AFM probes professor and robot wish everyone a happy Thanksgiving holiday

Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy

Nano-piezoelectric materials such as 1D piezoelectric nanofibers, nanowires, and nanobelts have attracted a lot of research interest in recent years. *

Because of their active property that can transform strain energy into electricity, 1D piezoelectric nano-materials can be building blocks for nano-generators, strain sensors, acoustic sensors, force sensors, biosensors, self-powered drug delivery systems, piezoelectric transistors and other intelligent systems. *

The most important property of these active materials is their ability to convert mechanical energy into electrical energy and vice versa. *

Therefore, researchers started developing nano-sized piezoelectric materials in hope of achieving better piezoelectric properties. *

The characterization of these piezoelectric properties, especially measuring the piezoelectric strain coefficients, remains a challenge. *

The Atomic Force Microscopy (AFM)-based method to directly measure nano-materials’ piezoelectric strain coefficients is widely used.

However, several factors such as the extremely small piezoelectric deformation, the influence from the parasitic electrostatic force, and the environmental noise can make the measurement results questionable. *

In the article “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” Guitao Zhang, Xi Chen, Weihe Xu, Wei-Dong Yao, and Yong Shi address these issues by introducing a resonant piezo-force microscopy method and describing how it was used to accurately measure the piezoelectric deformation from 1D piezoelectric nanofibers. *

During the measurement the AFM tip was brought into contact with the piezoelectric sample and set to work close to the AFM tip’s first resonant frequency. *

The AFM probe used in this test was a platinum iridium coated NanoWorld Arrow-CONTPt (typical force constant 0.2 N/m, typical resonant frequency 14 KHz. The PtIr coating makes the AFM tip conductive and at the same time enhances the laser reflection from the detector facing side of the AFM cantilever to the photodetector. *

A lock-in amplifier was used to pick up the sample’s deformation signal at the testing frequency. By using this technique, the piezoelectric strain constant d33 of the Lead Zirconate Titanate (PZT) nanofiber with a diameter of 76 nm was measured. The result showed that d33 of this PZT nanofiber was around 387 pm/V. Meanwhile, by tracking the piezoelectric deformation phase image, domain structures inside PZT nanofibers were identified. *

Figure 5 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. : Piezoelectric deformation amplitude image from a PZT nanofiber on a silicon dioxide substrate (a) and its cross-sectional view along the horizontal direction (b). Conductive NanoWorld Arrow-CONTPt AFM probes were used for the resonant piezo-force microscopy
Figure 5 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. :
Piezoelectric deformation amplitude image from a PZT nanofiber on a silicon dioxide substrate (a) and its cross-sectional view along the horizontal direction (b).

 

Figure 6 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. : (a) Piezoelectric deformation phase image from a PZT nanofiber on the silicon dioxide substrate and its 3D image (b). NanoWorld Arrow-CONTPt platinum iridium 5 coated AFM probes were used.
Figure 6 from “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang et al. :
(a) Piezoelectric deformation phase image from a PZT nanofiber on the silicon dioxide substrate and its 3D image (b).

*Guitao Zhang, Xi Chen, Weihe Xu, Wei-Dong Yao and Yong Shi
Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy
AIP Advances 12, 035203 (2022)
DOI: https://doi.org/10.1063/5.0081109

The article “Piezoelectric property of PZT nanofibers characterized by resonant piezo-force microscopy” by Guitao Zhang, Xi Chen, Weihe Xu, Wei-Dong Yao and Yong Shi is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/.