基于巨型磁阻的Allegro IC（GMR）
基于巨型磁阻的Allegro IC（GMR）
By Bryan Cadugan,
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Abstract
Allegro MicroSystems is a world leader in developing, manufacturing, and marketing high-performance集成电路（IC）, which incorporate high performance magnetic transducers. This whitepaper provides a basic understanding of the giant magnetoresistance (GMR) effect and how Allegro uses this technology in market-leading ICs to meet today’s application requirements.
巨型磁阻（GMR）效应
GMR效应于1988年由Albert Furth ofUnitéMixtedemeiqueCNRS/ Thales和Petergrünbergoftsitutfürfeskörperforschungforschungszentrumjülichgmbh。这两个人在2007年赢得了诺贝尔这一发现的奖励。GMR效应的基本原则是基于电子旋流。在磁阻器中，电子散射率随着电子的旋转状态的相互作用和电子正在行进的介质的磁取向而增加或减小。电子散射增加了电子流的平均自由路径，有效改变介质的电阻。总之，磁阻器是在磁场存在下改变其电阻值的电阻器。
通过产生由不同磁性和非磁性材料制成的非常薄层的序列来制造GMR换能器。这些材料的序列和厚度使得薄膜（GMR堆叠）堆叠在磁场存在下改变其电阻。
Over time, advances in GMR led to the development of a “spin-valve” type structure, which is what Allegro uses in their newest ICs. In a spin-valve, one of the two magnetic layers is considered a “reference” and is pinned or fixed in its orientation, and the other is called a “free” layer and is free to align with the magnetic field in the surrounding environment (see Figure 1). In typical magnetic sensor applications, this magnetic field is generated by a magnet or an electrical current, and is referred to as Bappthroughout the remainder of this document. The “spin-valve” is so named because it resembles a faucet, where the flow of water is related to the degree of rotation of the spigot. The open position for a GMR spin-valve relates to when themagnetic layers are aligned (as shown in Orientation A in Figure 1) where the resistance is lowest. The closed position (or low flow position) occurs when the magnetic layers are anti-aligned (as shown in Orientation B in Figure 1) where the resistance is highest. For any angular difference between the “reference” and “free” layers, the resistance of the GMR transducer is proportional to the cosine of this angle.
R = Rmin+ (Rmin– Rmax) × cos(θ)
The % of change in resistance is called the MR%, or magnetoresistive percentage. Allegro’s GMR transducers typically have MR% in the range of 5% to 8% for the full range of field response. This level of response creates a signal about 50 times higher than Allegro’s Hall-effect transducers, enabling a higher signal-to-noise level in ICs using GMR transducers instead of Hall-effect transducers.
GMR响应
GMR到应用领域的本机响应（Bapp）在电阻器的平面中（因此模具表面或IC表面）与施加磁性角度的余弦成比例
field. However, the resistance value of the GMR does not always indicate the strength of the field. A basic GMR transducer is more of a magnetic angle sensor (as shown in Figure 1). However, in
许多情况下，从GMR换能器期望对一个轴上的场的线性响应。为了创建此线性响应，从“参考”层中创建了90度的各向异性
acts like another magnetic field to be vector summed with the applied field (this anisotropy-induced field, Ban, is indicated by yellow arrow in Figure 2). The response then has a linear region around the state of zero magnetic field. This method of linearizing the response is used in many of Allegro’s ICs. It is important to note the saturated response present at either extreme of the range of field response. When in a linear application, the maximum operating range is specified to account for stray magnetic field and the magnetic stimulus to be sensed. GMR product datasheets can be referenced to indicate the operating boundary conditions. One item of note is that Allegro Hall-effect solutions have no such native saturated response. Allegro’s Hall ICs have a saturated response based on application or electrical circuit conditions, not a result of the Hall technology itself.
Using GMR in an IC Application
Typically, GMR resistors are created and placed in a Wheatstone bridge configuration. Half of the Wheatstone bridge (elements A and C in Figure 3) is positioned under one magnetic condition
并且，惠斯通桥（元件B和D）的另一半位于另一种磁性条件下。理想地，这些条件呈现相同但相反的响应，允许来自桥梁的最大输出信号。如图3所示，图3中的蓝色箭头和文本所示，元素A和C感应指向左侧的方向（在此示例中的反并行状态，表示为R.max在图1）中，元件B和D感应在指向右侧的方向上的字段（在该示例中的并行状态下，表示为rminin Figure 1). The result is that resistors A and C will be in a high resistance state and those in B and D will be in a low resistance state. The differential output will then be positive.
使用惠斯通桥，输出始终与应用的v缩放CC并且没有施加磁场，在0V的差分输出中心。然后根据惠斯通桥上的应用磁场的方向，差动桥输出将正面或负面地摆动。该桥接配置允许消除温度效应以及对杂散磁场的免疫水平。
对于电流传感器，现场在一个方向上以惠斯通桥的元件A和C转向，以及符合惠斯通桥的ElementB和D的磁场（参见
图4）。惠斯通桥的输出被馈送到差分放大器，然后通过Allegro的正常灵敏度和偏移校正电路，以及模拟或数字域中的可能更先进的信号处理电路。在未集成导体的其他雷竞技最新网址应用中，GMR元件的物理空间分离用于影响差动
signal, allowing response to a variety of magnetic stimulus.
GMR的另一个应用程序是用于环杂志net speed sensing applications such as ABS or transmission sensors. A ring of magnetic material is created with alternating north and south magnetization as shown in Figure 5. The GMR sensor may be placed under this material such that the plane of the die is horizontal. The spacing between the A and C GMR elements and B and D GMR elements creates a different magnetic field sensed by these sets of elements based on where the ring magnet is in its rotational cycle. When an N (north) pole is centered over the die, the magnetic field is pointing to the left over elements A and C and to the right over elements B and D. This will create a response on the GMR as noted in Figure 3, with a maximum positive response out of the GMR bridge. When over an S (south) pole, the response will be maximally negative. When between poles, the field is about equal for each element and the response of the bridge is near 0. This results in a sinusoidal output from the sensor as the ring magnet rotates. By counting the time between thresholds in the output over time, the speed of the ring magnet can be measured. The higher sensitivity of the GMR compared with traditional Hall sensors provides the capability for much higher air gap sensing, as well as much higher repeatability in the output for higher precision in the speed output.
Allegro Has a Monolithic GMR Solution
Many vendors selling GMR solutions do so using a multi-chip approach: a “sensor” chip and an “interface” chip. Allegro is one of very few IC manufacturers who directly integrate GMR technology
在他们的半导体晶圆的顶部。
This integrated approach offers many advantages, including an improvement in reliability by avoiding additional die-to-die bonding, and allowing for a simpler overall design when integrating current carrying lines or positioning the elements versus an external reference.
晶片进入包裹
Since Allegro’s GMR solution is monolithic in nature, GMR IC wafers are managed in the same manner as Hall-effect sensors IC wafers. The fabricated wafers are ground to the proper thickness for their packages, and the wafer is cut into the appropriate die size. Following this step, the part is packaged in Allegro’s standard range of semiconductor IC packages.
选择一个大厅的解决方案或GMR解决方法n
GMR换能器提供一些优势，优于霍尔效应传感器。然而，了解这些换能器的所需应用非常重要，如在许多情况下，霍尔溶液是更好的解决方案。
| 因素 | 大厅 | GMR（基于 example stack) |
| Sensitive direction | 通过平面（1轴） | In plane (2 axis), usually 1 primary |
| 回复 | Perfectly one axis linear | 余弦类型响应 在2个轴上更多 complex to interpret |
| Sensitivity (native) | 〜10-20μV/ g | 0.5-2 mV / g （50+ x大厅） |
| 线性范围 | Unrestricted | ±55 G |
| 响应范围 | Unrestricted | ±100 G |
结论
Allegro’s new integrated GMR technology provides an additional tool in the designer’s toolbox to address new applications and to extend the capabilities of their ICs in existing applications. GMR offers the ability to improve signal to noise, increase resolution, or reduce the required field level for a given solution (smaller magnets, larger air gaps, etc.). Additionally, sensing in-plane to the wafer or IC surface gives the ability to create new, more robust, differentially magnetic solutions than possible with through-plane sensitive Hall technology. Allegro will be releasing products across all relevant magnetic sensor IC portfolios to take advantage of the new capability that GMR technology provides.