PiezoElectric MEMS Technology

Blog Credit : Trupti Thakur

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PiezoElectric MEMS Technology

 

A group of researchers at the Indian Institute of Technology Madras and the Defence Research and Development Organisation (DRDO) has successfully developed a new sensor technology for underwater communications. The technology can be applied by the Navy and has the potential to revolutionize underwater communication technology.

Development of Piezoelectric MEMS Technology

Piezoelectric MEMS technology is an important component for developing high-performance thin films that can be used for acoustics and vibration-sensing applications. Researchers at the DRDO and IIT Madras have successfully created the piezo MEMS process recipe for the complete fabrication of an acoustic sensor. The PZT thin film-based acoustic sensor they fabricated exhibits higher performance than the conventional PVDF-based acoustic sensor.

Advantages of Indigenous Technology

One of the significant advantages of this indigenous technology is that the cost of fabrication is relatively lower than international foundries, which have limited foundries available. The Navy can use this technology to fabricate high-performance piezo MEMS acoustic devices at a lower cost. This technology also enables researchers to develop devices that are more advantageous for defence applications.

Challenges of Piezoelectric MEMS Technology

The piezo MEMS process technology is not without its challenges, which include the need for high reliability and durability in harsh underwater environments, high pressure, and the corrosive nature of seawater. Developing technology that can withstand these challenges is crucial for improving the performance of piezo MEMS devices.

Significance of the Piezo Thin Film

The piezo thin film is an essential component of piezo MEMS devices as it enables the conversion of mechanical energy into electrical energy. The successful development of the piezo MEMS process recipe means that researchers can fabricate acoustic sensors without degrading the functionality of the piezo thin film. The fabricated sensors exhibit higher performance than conventional sensors, making them ideal for use in harsh underwater environments.

Potential Applications of Piezo MEMS Devices

Piezo MEMS devices have a range of applications in acoustics and vibration-sensing, making them useful in the development of underwater communication devices. The Navy can use these devices to enhance communication and sensing in harsh underwater environments to ease their operations and capability.

A piezoelectric microelectromechanical system (piezoMEMS) is a miniature or microscopic device that uses piezoelectricity to generate motion and carry out its tasks. It is a microelectromechanical system that takes advantage of an electrical potential that appears under mechanical stress. PiezoMEMS can be found in a variety of applications, such as switches, inkjet printer heads, sensors, micropumps, and energy harvesters.

Development

Interest in piezoMEMS technology began around the early 1990s as scientists explored alternatives to electrostatic actuation in radio frequency (RF) microelectromechanical systems (MEMS) For RF MEMS, electrostatic actuation specialized high voltage charge pump circuits due to small electrode gap spacing and large driving voltages. In contrast, piezoelectric actuation allowed for high sensitivity as well as low voltage and power consumption as low as a few millivolts. It also had the ability to close large vertical gaps while still allowing for low microsecond operating speeds. Lead zirconate titanate (PZT), in particular, offered the most promise as a piezoelectric material because of its high piezoelectric coefficient, tunable dielectric constant, and electromechanical coupling coefficient. PiezoMEMS have been applied to various different technologies from switches to sensors, and further research have led to the creation of piezoelectric thin films, which aided in the realization of highly integrated piezoMEMS devices.

The first reported piezoelectrically actuated RF MEMS switch was developed by scientists at the LG Electronics Institute of Technology in Seoul, South Korea in 2005. The researchers designed and actualized a RF MEMS switch with a piezoelectric cantilever actuator that had an operation voltage of 2.5 volts.

In 2017, researchers from the U.S. Army Research Laboratory (ARL) evaluated the radiation effects in the piezoelectric response of PZT thin films for the first time. They determined that PZT exhibited a degree of radiation hardness that could be further extended by using conductive oxide electrodes instead of traditional platinum electrodes. Gamma radiation tests have also shown that actuated devices such as switches, resonators, and inertial devices could benefit from the radiation tolerance of PZT, suggesting the possibility that actuators and sensors can be integrated into platforms evaluating nuclear material and reduce human exposure to radiation.

This experiment was part of a decades-long research investment effort at ARL to improve the use of PZT thin film technology for piezoMEMS. Other piezoMEMS-related work included developing a piezoelectric microphone based on PZT thin films, creating new integrated surface micromachining processes for RF MEMS to incorporate thin film PZT actuators, providing the first experimental demonstration of monolithically integrated piezoMEMS RF switches with contour mode filters, and demonstrating the feasibility of vibrational energy harvesting using thin film PZT MEMS. In their work, researchers from ARL have also increased the overall electromechanical response of PZT thin films by 15-30% by incorporating iridium oxide electrode materials.

 Design

There exists three primary approaches to realizing PiezoMEMS devices:

1. The additive approach:The piezoelectric thin films are deposited on silicon substrates with layers of insulating and conducting material followed by surface or silicon bulk micromachining.
2. The subtractive approach:Single crystal or polycrystalline piezoelectrics and piezoceramics are subjected to direct bulk micromachining and then electrodes.
3. The integrative approach:Micromachined structures are integrated in silicon or piezoelectrics by using bonding techniques on bulk piezoelectric or silicon substrates.

PiezoMEMS use two principal crystal structures, the wurtzite and perovskite structures.

 Challenges

PiezoMEMS still face many difficulties that impede its ability to be successfully commercialized. For instance, the success of depositing uniform films of piezoelectrics still depend heavily on the use of appropriate layers of proper nucleation and film growth. As a result, extensive device-specific development efforts are needed to create a proper sensor structure. In addition, researchers continue to search for ways to reduce and control the material and sensor drift and aging characteristics of thin film piezoelectric materials. Deposition techniques to create thin films with properties approaching those of bulk materials remain in development and in need of improvement. Furthermore, the chemistry and etching characteristics of most piezoelectric materials remain very slow.

 

 

Blog By : Trupti Thakur