Magnetic tunnel junctions (MTJs) have received tremendous interest since the discovery of substantial room temperature
tunneling magnetoresistance (TMR) due to spin-dependent tunneling, and have been intensively investigated for
applications in next-generation memory devices, hard disk drives, and magnetic sensors. In the fabrication of MTJs,
etching is needed to remove the top cap layers, upper magnetic layers, and the middle oxide layer in order to form a
tunneling junction. In view of this, we have devised an innovative, simple, low-cost endpoint detection method for
fabricating MTJs. In this method, the endpoint is detected by measurement of the sheet resistance of the MTJ stack. Only
a multimeter is needed in this method, hence it provides a simple low-cost alternative for spintronic device researchers to
explore the research field of magnetic tunnel junctions. This technique is also of great use in other kinds of metallic stack
etching experiments.
In this paper, two lithographic fabrication processes for magnetic tunnel junctions (MTJs) with different mask designs and etching technologies are discussed. The advantages and disadvantages of both processes are compared. The crucial steps to protect the oxide insulating barriers and avoid side-wall redepositions (which may lead to short circuits) are developed, and important design considerations of the mask patterns and the device geometric structures are elaborated. We show that implementing the strategies developed greatly increases the successful manufacturing yield of MTJ magnetoelectronics devices.
In this paper, we discuss the structural design including the materials, junction areas, and magnetic layers thicknesses,
and various noise sources including Johnson noise, shot noise, 1/f noise, and thermal magnetic noise, that must be
considered when building a magnetic tunnel junction (MTJ) magnetic field sensor with the goal of SQUID-like
sensitivity. Analytical derivations of the sensor sensitivity and different noise sources are provided. A highly-portable
software design tool is developed to optimize the various parameters of the sensor design, while also predicting the
expected sensitivity, operating frequency range, operating current and power of the finished sensor. The functions and
operations of this design tool are described. The relationships between the sensor detectivity and some critical design
parameters are studied with this design tool. A possible design for the construction of an ultrasensitive magnetic field
sensor is proposed.
The discovery of tunneling magnetoresistance (TMR) has enhanced the magnetoresistance (MR) ratio from the giant
magnetoresistance (GMR) regime of around 10% to over 400% at room temperature. A combination of magnetic tunnel
junctions with high magnetoresistance ratio and soft magnetic layers enables the development of ultra-low magnetic field
sensor with sensitivity down to the scale of picoTesla. A magnetic field sensor with such high sensitivity would have
important applications in biomedicine, information storage, and remote sensing such as higher resolution images for
cardiograph and magnetic resonance imaging and thus earlier detection of abnormal health condition; higher hard-disk
density; and remote sensing of metallic objects. We have constructed an automated four-probe electrical measurement
system for measuring TMR of magnetic tunnel junctions with high throughput, enabling us to optimize the properties of
the devices. Magnetron sputtering is used to deposit thin films with thickness ranged from angstroms to nanometers.
Photolithography and ion plasma etching are applied to pattern the devices. The devices have a range of size from 10 μm
x 10 μm to 80 μm x 80 μm. The device is composed of the bottom electrode, free soft magnetic layer, insulating oxide
layer, pinned layer, pinning layer, and top electrode. The magnetization of the free layer can be rotated by the external
magnetic field which in turn changes the resistance of the device and provide the sensing capability. The system structure,
design consideration, fabrication process, and preliminary experimental results are discussed and presented in this paper.
The advancement of the technology of magnetic tunnel junctions (MTJs) greatly hinges on the optimization of the
magnetic materials, fabrication process, and annealing conditions which involve characterization of a large number of
samples. As such, it is of paramount importance to have a rapid-turnaround characterization method since the
characterization process can take even longer time than the fabrication. Conventionally, micropositioners and probe tips
are manually operated to perform 4-point electrical measurement on each individual device which is a time-consuming,
low-throughput process. A commercial automatic probe card analyzer can provide high turnaround; however, it is
expensive and involves much cost and labor to install and maintain the equipment. In view of this, we have developed a
novel low-cost, home-made, high-throughput probe card analyzer system for characterization of MTJs. It can perform
fast 4-probe electrical measurements including current vs voltage, magnetoresistance, and bias dependence
measurements with a high turnaround of about 500 devices per hour. The design and construction of the system is
discussed in detail in this paper.
Traditionally, the common window method is used to quantify image quality in optical lithography. The common window method can take dose variation, focus error, mask critical dimension error and aberrations into account. However, the demerit of the common window method is its computation time. In this paper, a new metric called Normalized Process Latitude (NPL) is proposed. The NPL considers dose variation, focus error, mask critical dimension error and aberrations to output its final quantification value. Its processing time for quantifying one feature is usually within 10 seconds on a PC with 1 GHz CPU and 256 MB DRAM. We perform several comparisons between the total window value and the NPL. It is found that the NPL draws similar conclusion as the total window. We can conclude that NPL is a sensible figure of merit for image quantification.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.