Features of the receiving of piezoelectric thin films by plasma spraying of powdery AlN
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-03-03 |
| Journal | Russian Technological Journal |
| Authors | В. С. Фещенко, K. N. Zyablyuk, Э. А. Сенокосов, В. И. Чукита, Д. А. Киселев |
| Institutions | University of Science and Technology, Institute of Radio-Engineering and Electronics |
| Citations | 8 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: AlN Piezoelectric Films on Diamond Substrates
Section titled “Technical Documentation & Analysis: AlN Piezoelectric Films on Diamond Substrates”Executive Summary
Section titled “Executive Summary”This research successfully demonstrates a low-temperature plasma spraying method for depositing highly oriented, piezoelectric Aluminum Nitride (AlN) thin films, validating the critical role of high-quality diamond substrates in advanced microelectronics.
- Low-Temperature Compatibility: AlN films (200 nm thick) were deposited at substrate temperatures not exceeding 300 °C, ensuring compatibility with standard silicon (CMOS) semiconductor processing.
- Superior Substrate Performance: Single Crystal Diamond (SCD) and Silicon (Si) substrates yielded AlN films with significantly lower surface roughness (Ra < 0.3 nm) compared to polycrystalline Sitall (Ra = 4.64 nm).
- High Piezoelectric Quality: AlN films deposited on diamond achieved a piezoelectric coefficient ($d_{33}$) of 2.2 pm/V, corresponding to 60% of the value for a single-domain single-crystal reference sample.
- Crystallographic Orientation: IR spectroscopy confirmed the resulting polycrystalline AlN layers exhibited the desired strong (002) crystallographic orientation, crucial for maximum piezoelectric response.
- Methodology: The films were produced using a modified VUP-5M vacuum post utilizing 13.56 MHz RF plasma sputtering of powdered AlN targets.
- Application Potential: The resulting high-quality piezoelectric layers are suitable for manufacturing advanced micro- and nanoelectronic devices, including piezoelectric sensors and ultrasonic emitters.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Deposited Film Material | AlN (Aluminum Nitride) | N/A | Piezoelectric layer |
| Film Thickness | 200 | nm | Resulting layer thickness |
| Substrate Temperature (Max) | ≤ 300 | °C | Low-temperature process advantage |
| Piezoelectric Coefficient ($d_{33}$) on Diamond | 2.2 | pm/V | 60% of single-domain reference |
| Piezoelectric Coefficient ($d_{33}$) on Silicon | 7.2 | pm/V | High-oriented multi-domain structure |
| Surface Roughness (Ra) on Diamond | 0.27 | nm | Arithmetic average roughness |
| Surface Roughness (Rms) on Diamond | 0.45 | nm | Root Mean Square roughness |
| Preferred Orientation | (002) | N/A | Confirmed by IR spectroscopy |
| Sputtering Gas Pressure (Ar) | 0.5-0.7 | Pa | Argon working pressure |
| RF Sputtering Frequency | 13.56 | MHz | High-frequency generator used |
| Deposition Rate | 300 | nm/hour | Measured sputtering speed |
| DC Bias Voltage (Auto-bias) | -120 to -180 | V | Applied during deposition |
| IR Absorption Peak | 672 | $\text{cm}^{-1}$ | Corresponds to E1(TO) phonon mode |
Key Methodologies
Section titled “Key Methodologies”The AlN thin films were produced using a modified VUP-5M vacuum post equipped with a custom RF magnetron sputtering system.
- Equipment Modification: The VUP-5M system was upgraded with an RF generator (13.56 MHz, up to 1.5 kW) and a water-cooled magnetron attachment designed for dielectric targets.
- Target Preparation: The AlN target was fabricated by depositing a 0.3-0.4 mm thick layer of AlN powder (A100 grade) onto a 0.5 mm thick AlN ceramic base.
- Substrate Preparation: Substrates used included single crystal diamond (SCD, pre-coated with Platinum), single crystal Silicon (Si), and polycrystalline Sitall.
- Process Parameters: Argon gas was introduced at a pressure of 0.5-0.7 Pa. The substrate holder was heated and maintained at 300 °C.
- Plasma Control: Plasma power was controlled by tuning variable capacitors (C5 and C6) in the matching network, monitored via forward wave (FW) and reflected wave (RW) detectors.
- Deposition Cycle: The deposition rate was approximately 300 nm/hour. Due to target contamination issues (metallic aluminum formation), films thicker than 300 nm required multi-stage deposition with intermediate target cleaning.
- Characterization: Films were analyzed using Infrared (IR) spectroscopy to confirm (002) orientation and Scanning Probe Microscopy (SPM) to measure surface roughness and local piezoelectric coefficient ($d_{33}$).
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research highlights that achieving high-quality piezoelectric AlN films is critically dependent on the substrate’s surface quality and material properties, particularly thermal conductivity and crystalline structure. 6CCVD is uniquely positioned to supply the advanced diamond substrates and metalization required to replicate and extend this high-performance research.
Applicable Materials
Section titled “Applicable Materials”The superior results achieved on diamond substrates (lowest roughness, high $d_{33}$) directly align with 6CCVD’s core product offerings:
- Optical Grade Single Crystal Diamond (SCD): Required to replicate the high-quality template used in this study. 6CCVD provides SCD plates with exceptional surface quality (Ra < 1 nm polishing standard) and high thermal conductivity, essential for managing heat during the plasma process and ensuring device stability.
- Polycrystalline Diamond (PCD) Substrates: For large-area piezoelectric arrays or ultrasonic transducers where cost-effectiveness is key, 6CCVD offers inch-size PCD wafers (up to 125 mm) with polishing down to Ra < 5 nm, providing a superior alternative to Sitall or standard ceramics.
Customization Potential
Section titled “Customization Potential”The success of AlN deposition relies heavily on the interface layer (e.g., Platinum in this study). 6CCVD offers comprehensive material engineering services to optimize this interface for maximum piezoelectric performance.
| Requirement from Research | 6CCVD Custom Capability | Technical Advantage |
|---|---|---|
| Substrate Material | SCD and PCD plates up to 125 mm | Enables scaling of high-performance piezoelectric devices. |
| Substrate Thickness | SCD (0.1 µm to 500 µm) and Substrates (up to 10 mm) | Allows precise tuning for acoustic impedance matching in SAW/BAW devices. |
| Electrode Layer | Custom Metalization (Au, Pt, Pd, Ti, W, Cu) | We can replicate the Pt layer used, or engineer advanced stacks (e.g., Ti/Pt/Au) for improved adhesion and electrical contact stability. |
| Surface Finish | Ultra-low roughness polishing (Ra < 1 nm for SCD) | Essential for minimizing scattering losses and ensuring uniform (002) orientation in subsequent AlN deposition. |
| Custom Geometry | Laser cutting and shaping services | Provides custom dimensions and features necessary for integrating AlN sensors into complex micro-systems. |
Engineering Support
Section titled “Engineering Support”The challenges noted in the paper—such as target contamination and the strong dependence of film quality on substrate material—underscore the need for expert material consultation.
6CCVD’s in-house PhD engineering team specializes in the integration of thin films onto diamond platforms. We offer dedicated support for projects involving:
- Piezoelectric/Acoustic Devices: Optimizing material selection for high-frequency Surface Acoustic Wave (SAW) and Bulk Acoustic Wave (BAW) resonators.
- Thermal Management: Utilizing diamond’s superior thermal properties to enhance the power handling and stability of AlN-based ultrasonic emitters.
- Interface Engineering: Assisting researchers in designing optimal metalization stacks to control AlN polarity and maximize the effective piezoelectric coefficient ($d_{33}$).
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Оne of the promising materials in solid state electronics is the AlN compound. A wide range of semiconductor devices are produced from it, such as photodetectors, LEDs, piezoelectric converters, etc. But the widespread use of products based on AlN prevents low manufacturability designs based on it. In this regard, the development of new technologies for the production of devices based on AlN is relevant.The work is devoted to the study of thin AlN films obtained by plasma spraying from AlN powder. The review of existing technologies of production of thin films AlN is carried out.Their advantages and disadvantages are discussed. Information on the modernization of the VUP-5 installation, which allowed to spray the AlN film from the powdered state, is given.One of the significant advantages of the process developed in this work is that the substrate is heated to temperatures no higher than 300 oC, which in turn allows to combine this technology with the technology of silicon semiconductor devices.As a result, films with a thickness of 200 nm on various substrates were obtained and their surface structure was studied. It is shown that AlN films deposited on single crystal substrates such as diamond and silicon have the least roughness, while films on sitall have the worst roughness.The transmission spectra of the obtained AlN films were investigated by IR spectroscopy. With their help, it was shown that a polycrystalline AlN layer oriented in the crystallographic direction 002 is formed on the substrate. The piezoelectric properties of the obtained films were investigated by scanning probe microscopy. It is shown that their piezoelectric coefficient d33 is 60% of the value for a single-domain single-crystal sample for a diamond substrate, which indicates a sufficiently high quality of the resulting film.It is concluded that, although the quality of the layers strongly depends on the substrate, nevertheless, they exhibit a significant piezoelectric effect, which allows the use of this method for the manufacture of piezoelectric sensors, ultrasonic emitters, etc.