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New approaches offer the promise of providing energy efficient, low cost, small, and highly sensitive magnetic sensors. However, the 1/f noise of these new types of sensors is a major obstacle. Many army applications, such as detecting moving targets, require sensitivity at low frequencies. This paper reports development of a device, the MEMS flux concentrator, invented at ARL, that minimizes the effect of 1/f noise in sensors. The device accomplishes this by shifting the operating frequency to higher frequencies where 1/f noise is much lower. This shift is accomplished by modulating the magnetic field before it reaches the sensor. In our device, the magnetic sensor, a GMR sensor, is placed between flux concentrators that have been deposited on MEMS flaps. The motion of the MEMS flaps modulates the field by a factor of 3 at frequencies from 8 to 15 kHz. The MEMS flux concentrator should increase the sensitivity of many magnetic sensors by two to three orders of magnitude. An equally important benefit is that, because it is a modulation technique, it eliminates the problem of dealing with the large DC bias of most magnetoresistive sensors.
This report discusses the magnetic modeling results of a proof of concept system for 1/f noise mitigation in "large" sensors. The 1/f noise reduction is achieved by rotating flux concentrators that shift the operating frequency of the sensor to higher frequencies where 1/f noise is lower. The goal is to design systems with magnetic flux concentrators that maximize the enhancement of the field and the percentage modulation of the field but minimize size. These issues in execution and necessary tradeoffs in performance are discussed, and magnetic modeling is presented, showing a clear road map to increased performance from the viewpoint of field enhancement and modulation.
This book provides the reader with a unique opportunity to understand the basic and applied research and technology areas that support applications to enable Transformational capabilities for US Soldiers. The research papers are in line with the theme of the 24th Army Science Conference: “Transformational Science and Technology for the Current and Future Force,” emphasizing the critical role of Science and Technology in addressing the significant challenges posed by Global War On Terrorism while simultaneously developing Transformational capabilities for the Future Force.
Discover the latest advances in spintronic materials, devices, and applications In Spintronics: Materials, Devices and Applications, a team of distinguished researchers delivers a holistic introduction to spintronic effects within cutting-edge materials and applications. Containing the perfect balance of academic research and practical application, the book discusses the potential—and the key limitations and challenges—of spintronic devices. The latest title in the Wiley Series in Materials for Electronic and Optoelectronic Applications, Spintronics: Materials, Devices and Applications explores giant magneto-resistance (GMR) and tunneling magnetic resistance (TMR) materials, spin-transfer torque and spin-orbit torque materials, spin oscillators, and spin materials for use in artificial neural networks. Applications in multi-ferroelectric and antiferromagnetic materials are presented as well. This book also includes: A thorough introduction to recent research developments in the fields of spintronic materials, devices, and applications Comprehensive explorations of skymions, magnetic semiconductors, and antiferromagnetic materials Practical discussions of spin-transfer torque materials and devices for magnetic random-access memory In-depth examinations of giant magneto-resistance materials and devices for magnetic sensors Perfect for advanced students and researchers in materials science, physics, electronics, and computer science, Spintronics: Materials, Devices and Applications will also earn a place in the libraries of professionals working in the manufacture of optics, photonics, and nanometrology equipment.
Progress on the development of a device, the MEMS flux concentrator, for mitigating the problem of 1/f noise in magnetic sensors will be presented. The MEMS flux concentrator essentially eliminates the effect of 1/f noise by increasing the operating frequency of the sensor to a frequency region where 1/f noise is small. This is accomplished by putting flux concentrators on MEMS structures whose motion modulates the magnetic field at the position of the magnetic sensor. Depending on the sensor, mitigating the effect of 1/f noise will increase the sensitivity of magnetic sensors by one to three orders of magnitude. Combining the MEMS flux concentrator with magnetic tunnel junctions with MgO barriers should lead to low cost magnetic sensors that are able to detect 1 pT signals at 1 Hz.
Micro and nano-electro-mechanical system (M/NEMS) devices constitute key technological building blocks to enable increased additional functionalities within Integrated Circuits (ICs) in the More-Than-Moore era, as described in the International Technology Roadmap for Semiconductors. The CMOS ICs and M/NEMS dies can be combined in the same package (SiP), or integrated within a single chip (SoC). In the SoC approach the M/NEMS devices are monolithically integrated together with CMOS circuitry allowing the development of compact and low-cost CMOS-M/NEMS devices for multiple applications (physical sensors, chemical sensors, biosensors, actuators, energy actuators, filters, mechanical relays, and others). On-chip CMOS electronics integration can overcome limitations related to the extremely low-level signals in sub-micrometer and nanometer scale electromechanical transducers enabling novel breakthrough applications. This Special Issue aims to gather high quality research contributions dealing with MEMS and NEMS devices monolithically integrated with CMOS, independently of the final application and fabrication approach adopted (MEMS-first, interleaved MEMS, MEMS-last or others).]
This book covers the main physical mechanisms and the different contributions (1/f noise, shot noise, etc.) behind electronic fluctuations in various spintronic devices. It presents the first comprehensive summary of fundamental noise mechanisms in both electronic and spintronic devices and is therefore unique in that aspect. The pedagogic introduction to noise is complemented by a detailed description of how one could set up a noise measurement experiment in the lab. A further extensive description of the recent progress in understanding and controlling noise in spintronics, including the boom in 2D devices, molecular spintronics, and field sensing, is accompanied by both numerous bibliography references and tens of case studies on the fundamental aspects of noise and on some important qualitative steps to understand noise in spintronics. Moreover, a detailed discussion of unsolved problems and outlook make it an essential textbook for scientists and students desiring to exploit the information hidden in noise in both spintronics and conventional electronics.
1/f noise is present in every aspect of nature. Sensors and read-out electronics have the ultimate detection limit set by the noise floor of the white noise. In order to increase signal-to-noise ratio (SNR) of low frequency signals buried by high 1/f noise, the signal can be up-converted to a high frequency signal that lies in the lower white noise regime of the sensing device. Mechanical modulation can be employed to move low frequency electronic signals to higher frequency region through the use of microresonators. This thesis has two goals: (1) develop and fabricate a hybrid micromechanical-magnetoresistive magnetic field sensor; and (2) design an electrometer to measure currents collected from air streams containing ionized nano-particles. First, we designed magnetoresistive-microelectromechanical systems (MR-MEMS) hybrid devices based on the monolithic integration of magnetic thin films and silicon-on-insulator (SOI) MEMS fabrication techniques. We used MgO-based magnetic tunnel junctions (MTJ) placed on a bulk micromachined silicon MEMS device to form a hybrid sensing device. The MEMS device was used to mechanically modulate the magnetic field signal detected by the MTJ, thereby reducing the effects of 1/f noise on the MTJ's output. Two actuator designs were investigated: cantilever and electrostatic comb-drive. The second component of the thesis presents a MEMS-based electrometer for the detection of small currents from ionized particles in a particle detection system for air-quality monitoring. One method of particle detection ionizes particles and then feeds a stream of charged particles into a Faraday cup electrometer. We replaced the Faraday cup with a filtering porous mesh sensing-electrode coupled to a MEMS electrometer with a noise floor below 1 fA rms. Experiments were conducted with fA level currents produced by 10 nm diameter particles within an airflow of 1.0 L/min. The MEMS electrometer was compared and calibrated using commercial electrometers and particle counters.