Microelectromechanical Systems Actuators Research Articles

Issues in the Flexible Integration of Sputter-Deposited PZT Thin Films with Polysilicon and Ti/Pt Electrode Layers for Use as Sensors and Actuators in Microelectromechanical Systems (MEMS)

ABSTRACTSputter-deposited piezoelectric lead zirconate titanate (PZT) thin films with Ti/Pt and polysilicon electrode layers are being investigated for use in Microelectromechanical Systems (MEMS). Existing research shows the nucleation of the perovskite phase of the PZT is linked to the lattice spacing of the underlying Pt electrode and/or seed layers, and is key in obtaining PZT layers with good piezoelectric/ferroelectric properties. Our research with piezoelectric PZT films on Ti/Pt electrode layers aims at employing these films to generate and receive acoustic waves in flexural plate wave devices (FPWs). Our experiments indicate the formation of a random polycrystalline perovskite phase is linked to the emergence of oriented <100> Pt grains within the dominant <111>-oriented crystal structure during rapid thermal annealing in an oxygen environment. Pt films annealed in nitrogen, in contrast, retained their <111> preferential orientation without the formation of Pt <100> grains. PZT films deposited on these electrodes and annealed in nitrogen were strongly oriented in the <111> direction, but exhibited lossy ferroelectric behavior and were prone to delamination. We are also investigating the feasibility of using doped polysilicon electrode layers with PZT thin films. The multiple layers used with the Pt electrode (Pt, Ti, and SiO2 adhesion layer) have significant interactions with one another, and replacing these layers with a single electrode layer should alleviate these complications. A low-temperature PZT deposition process (300°C) and short annealing cycles (30 sec.), coupled with a TiO2 barrier/seed layer should prevent interdiffusion and reactions between the polysilicon and PZT layers. Our experiments show that PZT films deposited and annealed on doped polysilicon layers develop a random polycrystalline perovskite phase, but are subject to tensile cracking. The use of polysilicon as an electrode layer should also facilitate the integration of piezoelectric PZT layers with polysilicon surface micromachined structures using SiGe sacrificial layers.

Computer-assisted tools and interventional technologies

and postoperative measurement of the surgical action. We cannot directly integrate these three phases because we lack sensitive and accurate devices to accurately gauge surgical practice. We ~lso lack functional modelling of the patient's anatomy and physiology to examine cause and effect of surgery or to optimise our actions before the patient presents to the operating room. During surgery, we cannot access or link precise preoperative plans directly with the execution of the surgical task. Our current tools do not provide accurate information to the surgeon to be acted on during the actual procedure. The next generation of surgical tools and interventional information technologies will include Closing the in surgical practice preoperative planners that allow fully functional, three-dimensional modelling of patients' anatomy and physiology. Surgeons will simulate the cause and effect of their surgery before it actually takes place. Most importantly, these preoperative simulators will permit the surgeon to optimise a surgical plan that will be anatomically and physiologically patient-specific. The surgical toolbox of the future will include robotic assistive devices, navigational and image-guided surgical tools, and microelectro-mechanical systems (MEMS), micromanipulators, and implantable sensors. Smart tools will help to optimise preoperative plans or adjust the plan during surgery as needed. These computer-assisted tools will enable surgeons to develop the next generation of minimally invasive surgical procedures. These technologies will allow us to directly link surgical practice to outcomes. Navigation systems and MEMS sensors and actuators will give continuous and updated information during surgery. Implantable sensors and actuators will permit the measurement of biological, physiological, and mechanical factors, and will allow readjustment of the implanted system by delivering biological materials or by readjusting the fit and alignment of an implant. Computer-assisted technologies will also enable development of a new concept of vision, allowing direct viewing of the patient's full three-dimensional anatomy without the need for ionising radiation during surgery. The development of these technologies and tools will not only complement the current efforts in genetic and biological therapies, but also will be absolutely necessary to their success. For example, treatment plans using gene or biological therapies such as growth factors will depend on developing accurate, responsive delivery systems to apply therapeutic agents to specific pathological areas without disrupting soft tissues or blood supply to the area. The promise of these computer-assisted tools extends beyond new hardware and software. One of the most important enabling features of these technologies is the ability to tightly couple and integrate preoperative planning and imaging, quanitfy surgical techniques, and directly relate patient's outcome to surgical practice--closing the loop in the treatment of patients (figure).These technologies will provide clinical researchers with the ability to quantify, characterise, and validate surgical practice. Our clinical and surgical tasks will no doubt evolve and adapt to the changing world and the needs of our patients. New tools and technologies will enable us to monitor patients almost at any time, anywhere, and on an outpatient basis in doctors' offices, and will allow earlier interventions, better monitoring, and more continuous care. These technologies will also validate surgical techniques in a more efficient manner, providing information that can be passed on to a larger surgical audience. Surgeons worldwide could then benefit from the improvements in surgical practice without necessarily having used the actual systems themselves. Information technologies and tools will not replace surgeons or the care that they provide. As stated by Bruce Burlington, Director of the US Food and Drug Administration's Center for Devices and Radiological Health, Medicine isn't an encounter with It's a human encounter, supported by technology. There is great potential for the application of this new approach and interventional information technologies in many subspeciahies within orthopaedic surgery, and in the entire field of surgery. Orthopaedic surgeons can be proud to have led the way in the last part of the 20th century in the development of the clinical use of computer-assisted technologies. These new technologies and tools are not an end in themselves but a means to permit surgeons to explore and create the next generation of surgical techniques. As we open the new millennium, we have no doubt that these enabling technologies will influence the way surgeons plan, simulate, execute, and measure surgical practice to benefit our patients, closing the in surgical practice.

Failure modes in surface micromachined microelectromechanical actuation systems

Abstract In order for the rapidly emerging field of MicroElectroMechanical Systems (MEMS) to meet its extraordinary expectations regarding commercial impact, issues pertaining to how they fail must be understood. We identify and address failure modes common to a broad range of MEMS actuation systems, including adhesion (stiction) and friction-induced failures caused by improper operational methods, mechanical instabilities, and electrical instabilities. Demonstrated methods to mitigate these failure modes include implementing optimized designs, model-based operational methods, and chemical surface treatments.

Application of MEMS technology in automotive sensors and actuators

Sensors and actuators are the critical system components that collect and act on information in the analog environment and link it to the world of digital electronics. The functional groups of sensors, software, controller hardware, and actuators from the backbone of present and future automotive systems. Unit volumes for sensors and actuators in the automotive industry are measured in millions per year and at a unit cost of a few dollars. The design of sensors and actuators has increasingly made use of microelectromechanical systems (MEMS) technology. This technology is well suited to producing a class of micromachined sensors and actuators that combines signal processing and communications on a single silicon chip or contained within the same package. This paper contains a discussion of the issues in producing MEMS sensors and actuators from the concept selection stage to the manufacturing platform. Examples of commercial and emerging automotive sensors and actuators are given, which illustrate the various aspects of device development. Future trends in MEMS technology as applied to automotive components are also discussed.