James A. Bain, Ph.D
Professor Bain’s Research, consists of two areas -
Heat Assisted Magnetic Recording (HAMR) and Near Field Transducers (NFT’s):
PIs: James A. Bain and Jonathan A. Malen
Students: Cheng‐Ming Chow, Joe Liang
Research Sponsors: Data Storage Systems Center (DSSC) and Sponsoring Companies, NSF
Heat Assisted Magnetic Recording (HAMR) is a candidate for use in magnetic recording systems operating at densities above 2 Tbits/in2. Today’s hard disk drives (HDD’s) operate at around 1 Tbits/in2, and are unlikely to reach 2 Tbits/in2 through extensions of the existing technology. The barrier is rather fundamental and is called the superparamagnetic limit. This limit arises with increasing storage density because shrinking the bit to raise the density also makes the bit more vulnerable to being disturbed by ambient thermal fluctuations. Thermal disturbance means that the recorded data will spontaneously disappear as bits flip randomly under thermal agitation. Making the bits out of magnetically “stiffer” material will suppress this thermally induced flipping. However, it will also make the medium too “stiff” to be able to be switched with the recording head. Thus the medium becomes unwritable, despite the fact that anything successfully written would be stable.
HAMR remedies the writability problem by delivering highly localized
thermal doses to the medium to “assist” in the writing process. In this
way, the very magnetically “stiff” medium is temporally “softened” during
writing. One very important challenge in this approach is to get the heat
sufficiently localized. A focused laser beam can make a hot spot of around
500 nm in diameter on the surface of a disk, and, indeed, is the technology
used in BlueRay optical disks. However, at 2 Tbits/in2, the bit size is about
35 nm x 8 nm, far below what could be heated with a focused optical laser.
Rather the hot spot created on the disk needs to be around 25 nm in
diameter, a factor of 20 smaller than focused optics will permit.
The work on near field transducers for HAMR seeks to develop nanoscale
dielectric and metallic structures that can guide light to the medium and
maintain a small optical profile. Highly integrated devices are desired that
can deliver stable optical output, dissipate power efficiently and withstand
parasitic heating of the NFT occurs during writing. An example of recent
work in this area (unpublished) is shown at right with a concept for the
entire light delivery system in a), fabrication results for standard
semiconductor lasers in b) and an innovative approach to stabilizing the
laser modes in c). Work to develop the resonator driven NFT is ongoing,
following a CMU patent listed below.
Selected Relevant Publications:
Some helpful publications for understanding the scope of the research directions with Prof Bain in the HAMR area are attached. An excellent overview is provided by Professor Mark Kryder and his team when he was Senior VP at Seagate (a little dated but still very relevant as a primer) . Recent publications by Bain and colleagues are attached as well that discuss nanoscale heat transfer between Au and dielectrics , two CMU patents detailing design innovations offered for HAMR near field transducers,  and , measurements of nanoscale heat transport in magnetic media, coupling light into plasmonic structures  and the role of media complex dielectric properties in determining coupling to the medium .
 M. H. Kryder et al., “Heat Assisted Magnetic Recording,” Proceedings of the IEEE, vol. 96, no. 11, pp. 1810–1835, Nov. 2008.
 M. Jeong et al., “Enhancement of Thermal Conductance at Metal‐Dielectric Interfaces Using Subnanometer Metal Adhesion Layers,” Phys. Rev. Applied, vol. 5, no. 1, p. 014009, Jan. 2016.
 E. J. Black, J. A. Bain, S. P. Powell, and T. E. Schlesinger, “Coupled Plasmonic Waveguides and Associated Apparatuses and Methods,” US20140099054 A1, 10‐Apr‐2014.
 J. A. Bain, M. J. Chabalko, T. E. Schlesinger, Y. Luo, and Y. Kong, “Dielectric Resonator Driven Near Field Transducer,” US20140050486 A1, 20‐Feb‐2014.
 H. Ho, A. A. Sharma, W. L. Ong, J. A. Malen, J. A. Bain, and J. Zhu, “Experimental estimates of inplane thermal conductivity in FePt‐C granular thin film heat assisted magnetic recording media using a model layered system,” Appl. Phys. Lett., vol. 103, no. 13, p. 131907, Sep. 2013.
 Y. Kong et al., “Evanescent Coupling Between Dielectric and Plasmonic Waveguides for HAMR Applications,” IEEE Transactions on Magnetics, vol. 47, no. 10, pp. 2364–2367, Oct. 2011.
 S. P. Powell, E. J. Black, T. E. Schlesinger, and J. A. Bain, “The influence of media optical properties on the efficiency of optical power delivery for heat assisted magnetic recording,” Journal of Applied Physics, vol. 109, no. 7, p. 07B775, Apr. 2011.
See this HAMR.pdf for papers referenced above.
Resistive Switching Devices for Memory Selectors, Memory Cells & RF Switches
PIs: James A. Bain (ECE), Marek Skowronski (MSE),
Students: Phoebe Yoeh, Darshil Gala, Yuanzhi Ma, Jonathan Goodwill, Liting Shen, Yuezhang
Research Sponsors: AFOSR, SRC, Intel, DARPA
NEW CLASSES OF SEMICONDUCTING MATERIALS
Amorphous chalcogenide and oxide semiconductors (and their
crystalline counterparts) offer wide potential application to emerging
electronics technology. These materials are leading candidates for
memory selectors (GeTe6, SiTeAsGe [STAG], TaHfOx), phase change
memory cells (PC‐RAM: GeSbTe [GST] and Al‐GST), Oxide Resistive
memory (RRAM: HfOx, TaOx) and RF switch elements (GeTe), among
others. What is attractive about these materials is that they can
reversibly change electrical conductivity over many orders of magnitude.
In some cases, this change is non‐volatile (but reversible) as in GST for
PC‐RAM or HfOx for RRAM. In other cases, this change is temporary
(i.e. volatile) as in the case of GeTe6 or TaHfOx for selector
applications. In this latter case, removal of electrical stimulus returns
the material to is high resistivity state.
While some of this behavior
is reasonably well understood,
much remains unclear. For
example, the nature of the
selector volatile ONstate has
been difficult to study as it is a
Additionally, interface electronic
states of these materials when
in contact with electrodes, the
dynamics of the volatile and
non‐volatile transformations, including the initiating and the rate‐controlling processes are all
understood in a very limited way. With understanding of these processes and materials physics will come the ability
to control these properties of interest.
Work in this project uses a specifically designed 11‐target chalcogenide and oxide sputter deposition system that co‐deposits alloy films from elemental targets (Figure 1) to develop and study resistive alloys as a function of composition. The focus of the work is on understanding their fundamental material properties. Special purpose scaled test structures are fabricated to measure electrical and structural properties at high speed and temperature. Figure 2 shows an example of a test structures made at CMU for applying simultaneous 5 ns thermal and electrical pulses to GST for measuring high speed crystallization dynamics. Additional modalities are using optical and magnetic stimuli to extract fundamental transport properties as a function of composition.
NOVEL DEVICE APPLICATIONS
As noted above, these materials enable many device applications, from non‐linear selectors to memory cells to RF switches. Work in this research area examines the links between material properties and device performance in an attempt to optimize devices. For example, Figure 3 on the next page shows studies of nanoscale HfOx devices where the hysteretic I‐V behavior is compared to structural changes within the device. Crystallization during the switching process is revealed. Similarly, Figure 4 shows an RF switch developed at CMU using GeTe as the switching material and a patterned W heater as the actuation element. Issues that have emerged from this work include the breakdown voltage of the materials as it limits power handling of the switches. Both of these represent new functionality that will be available in future electronic systems and must be optimized for functionality and performance.
Selected Relevant Publications:
Some recent publications of are attached for reference. These include description of the technique of using high speed electrical thermometry to characterize these devices  and , and the development of high speed external heaters , as well as the use of these techniques to study heating events and structural changes in devices . These papers also detail demonstrations of devices for advanced electronic systems like relaxation oscillators arrays , the development of the RF switch  and its use to create reconfigurable RF systems .
 M. Noman, A. A. Sharma, Y. Lu, M. Skowronski, P. A. Salvador, and J. A. Bain, “Transient characterization of the electroforming process in TiO2 based resistive switching devices,” Appl. Phys. Lett., vol. 102, no. 2, p. 023507, Jan. 2013.
 A. A. Sharma, M. Noman, M. Skowronski, and J. A. Bain, “High‐speed in‐situ pulsed thermometry in oxide RRAMs,” in Proceedings of Technical Program ‐ 2014 International Symposium on VLSI Technology, Systems and Application (VLSI‐TSA), 2014, pp. 1–2.
 M. Xu, G. Slovin, J. Paramesh, T. E. Schlesinger, and J. A. Bain, “Thermometry of a high temperature high speed micro heater,” Review of Scientific Instruments, vol. 87, no. 2, p. 024904, Feb. 2016.
 J. Kwon et al., “Transient Thermometry and High‐Resolution Transmission Electron Microscopy Analysis of Filamentary Resistive Switches,” ACS Appl. Mater. Interfaces, vol. 8, no. 31, pp. 20176– 20184, Aug. 2016.
 A. A. Sharma et al., “Low‐power, high‐performance S‐NDR oscillators for stereo (3D) vision using directly‐coupled oscillator networks,” in 2016 IEEE Symposium on VLSI Technology, 2016, pp. 1–2.
 N. El‐Hinnawy et al., “12.5 THz Fco GeTe Inline Phase‐Change Switch Technology for Reconfigurable RF and Switching Applications,” in 2014 IEEE Compound Semiconductor Integrated Circuit Symposium (CSICS), 2014, pp. 1–3.
 R. Singh et al., “A 3/5 GHz reconfigurable CMOS low‐noise amplifier integrated with a four‐terminal phase‐change RF switch,” in 2015 IEEE International Electron Devices Meeting (IEDM), 2015, p. 25.3.1‐25.3.4.
See this Resisitve Switching Devices.pdf for papers referenced above.