A Micro-Fluxgate Magnetic Sensor Using Closely Coupled Excitation and Pick-Up Coils
- PDF / 876,039 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 29 Downloads / 168 Views
A MICRO-FLUXGATE MAGNETIC SENSOR USING CLOSELY COUPLED EXCITATION AND PICK-UP COILS Won-Youl Choi, Kyoung-Won Na, Sung-Jin Ahn, and Sang-On Choi MEMS Laboratory, Samsung Advanced Institute of Technology (SAIT), Suwon, Korea ABSTRACT This paper presents a micro-fluxgate magnetic sensor composed of a rectangular-ring shaped magnetic core and solenoid excitation and pick-up coils. In order to improve the sensitivity of sensing element, the excitation and pick-up Cu coils are formed as a closely coupled structure. This unique coil structure allows to excite the magnetic core in an optimal condition with reduced excitation current. The 11 µm thick excitation and pick-up Cu coils were electroplated using Cr (300 Å) / Au (1500 Å) seed layer. The 2.9 µm thick Ni0.8Fe0.2 (permalloy) magnetic core layer was also electroplated with photoresist frame using sputtered Ni0.8Fe0.2 seed layer. The rectangular-ring shaped core was covered by photoresist and wet etching using dilute sulfuric acid. The magnetic core has a DC permeability of ∼1100 and coercive field of 0.1 Oe. The magnetic core is easily saturated due to the low coercive field and closed magnetic path for the excitation field. The chip size of the fabricated sensing element is 1.3 × 1.0 mm2. Excellent linear response over the range of –100 µT to +100 µT is obtained with 14 V/T sensitivity at excitation sine wave of 3 VP-P and 150 kHz. This low magnetic field sensing element is very useful for various applications such as: portable navigation systems including north-up and map data scrolling, military research, medical research, and space research.
INTRODUCTION A low magnetic field sensing and measuring have always been an essential function for numerous applications. The measure of the magnitude and direction of DC or low frequency AC magnetic field is more challenging than that of high frequency AC magnetic field. Various techniques and sensors have been developed to measure magnetic fields from 10-10 to 10-3 T. One of the most sensitive magnetic sensors is the fluxgate sensor [1-3]. Fluxgate sensors serve for the measurement of the magnetic field up to 1 mT with a resolution of 0.1 nT to 10 nT. They have broad application range from precise geophysical instruments to rugged detection sensors for security and military applications. The latest competitors of fluxgate sensor are anisotropic magnetoresistive (AMR) and newly developed giant magnetoresistive (GMR) magnetoresistors [4]. The main advantage of fluxgate sensor is its high temperature stability : 30 ppm/ temperature coefficient of sensitivity are easily achievable, while the same parameters for any other solid-state vectorial magnetic sensors (including semiconductors and magnetoresistors) are at least 10 times worse. However the conventional fluxgate sensor utilizes bulk or ribbon core, bobbins for the excitation and the pick-up, and electronic circuits for the core excitation and signal processing. These result in the disadvantages of large volume, large weight, and high cost. If the fluxgate sensor is develo
Data Loading...
