Achieving a stable laser power during HAMR operation is extremely challenging and has been a key gating item in achieving high performance and storage from HAMR HDDs. The laser power variation is mostly attributed to the change of its temperature. In this work, a detailed experimental study to measure and stabilize the laser diode temperature is conducted. Here, a novel approach is based on reverse bias usage of the laser diode to manage its temperature change during normal forward bias used in HAMR writing process. We demonstrate that reverse bias is used to pre-heat the laser diode to match the temperature of the laser diode in HAMR operation and suppress the laser power variations arising from mode hopping.

AbstractLaser-lubricant interaction has been a critical reliability issue in a thermo-tribological system named heat-assisted magnetic recording, one of the next generation hard disk drive solutions to increasing data storage. The lubricant response under laser irradiation and the subsequent lubricant recovery are crucial to the system’s reliability and longevity, however, they cannot be diagnosed locally and timely so far. Here, we propose a thermal scheme to in-situ characterize the mechanical laser-lubricant interaction. The nanometer-thick lubricant has a thermal barrier effect on the near-field thermal transport in the system, according to which the lubricant thickness can be determined. As demonstrations, this paper reports the first quantitative in-situ measurements of the laser-induced lubricant depletion and the subsequent reflow dynamics. The proposed scheme shows a sub-angstrom resolution (~0.2 Å) and a fast response time within seconds, rendering in-situ real-time lubricant diagnosis feasible in the practical hard disk drive products.

In this protocol, we present a facile nanoscale thermal mapping technique for electronic devices by use of atomic force microscopy and a phase change material Ge 2 Sb 2 Te 5 . We describe steps for Ge 2 Sb 2 Te 5 thin film coating, Ge 2 Sb 2 Te 5 temperature calibration, thermal mapping by varying heater power, and thermal mapping by varying heating time. The protocol can be applied for resolving surface temperatures of various operational microelectronic devices with a nanoscale precision. For complete details on the use and execution of this protocol, please refer to Cheng et al. 1

Heat assisted magnetic recording (HAMR) is one of the leading technologies for next generation magnetic recording. Laser heating is utilized in HAMR to achieve magnetic writing of the very high coercivity media. However, the high temperature environment creates several reliability challenges for the head disk interface (HDI). Material transfer within the HDI under HAMR conditions or emulated HAMR conditions has been studied by experiments and simulations. It is found that the material transfer is mainly driven by thermal gradient and mechanical interaction such as head disk contact. In this paper, we designed an experiment to investigate the material transfer from HAMR media to a flying magnetic head. It shows that thermal gradient, more specifically a hotter media and cooler head, is the driving force for the material accumulation on the head. Furthermore, we calibrated the media temperature by a phase change material to identify the critical temperature that triggers the material transfer process. This study is important to understand the smear formation mechanism in HAMR drives.

Heat-assisted magnetic recording (HAMR) is on the magnetic recording industry’s roadmap of next generation recording technology. The high temperature writing condition creates several reliability challenges for the head disk interface (HDI). Material buildup, or so-called smear, that accumulates between the head and the media is one key challenge. Our previous studies found that the material transfer is mainly driven by the high temperature and mechanical interaction between the head and media. In this paper, we systematically studied the role of the media in the smear formation and transfer process. We identified at least two different types of smear and the critical temperatures for their formation and transfer. Furthermore, we found that optimizing the media process, particularly the magnetic layer and lubricant, could help to reduce smear. This study helps in understanding the smear formation mechanism and explores methods to mitigate smear for HAMR drives.

Contamination, known as smear, in the head-disk interface poses a significant reliability challenge for heat-assisted magnetic recording (HAMR) technology. While smear in perpendicular magnetic recording (PMR) can induce head-disk spacing instability, light at the HAMR interface produces additional adverse effects on both head reliability and recording quality. Previous studies have demonstrated that optically absorbing smear, such as organic carbonaceous material, is particularly harmful since the heat dissipated at the interface raises the temperature of the near-field transducer (NFT), thereby compromising its reliability [1] , [2] . Due to the optical nature of the HAMR interface, the accumulation of metallic smear also presents a significant challenge. Metallic interface materials not only absorb light that is emitted from the NFT, but they can also redirect the path of the propagating plasmon generated at the surface of the NFT. This ability to perturb the near-field coupling to the medium has significant implications for the stability of the HAMR recording process. Thus, both the NFT reliability and recording impact must be investigated to determine the ramifications of metallic smear in HAMR. In this work, we utilize opto-thermal simulation to uncover metallic smear's impact on HAMR reliability and recording performance.

We have studied the reliability of a near-field transducer (NFT) embedded in a magnetic recording slider used for heat-assisted magnetic recording (HAMR) in hard disk drives with a linear velocity of 20 m/s. The NFT head structure and the disk are separated by an air film of 2 nm thickness. In this article, the magnetic write width and amplitude of the written magnetic signal on the disk are used as a "health monitor" for the reliability of the NFT under long-term thermal exposure. The results show that the reliability of the NFT head structure sharply decreases with increasing temperature of the NFT but depends only slightly on the media temperature.

In heat-assisted magnetic recording, minimization of optical laser power is important for the reliability of the head-disk interface. In this paper, a prototype heat-assisted magnetic recording system is used to investigate the relationship between the needed optical laser power and disk drive design parameters. In particular, the change of optical laser power, which is a function of the laser current, is investigated for different disk radii and write head flying heights while keeping the write width of the recorded signal constant. In addition, the dependence of laser power during writing is studied as a function of the thickness and material properties of a very thin “capping layer” on the top of the recording magnetic layer. The results show that laser power and media design parameters play a crucial role in heat-assisted magnetic recording devices.

Heat assisted magnetic recording (HAMR) is a promising technology for the next generation hard disk drives (HDDs). Understanding the heat transfer at nanoscales and implementing a proper thermal management scheme become very critical as a few heat sources and energy delivery components are compactly integrated in a HAMR drive. Recently, a back-heating experimental setup is used to study heat transfer behavior. It is found that the detection of head disk contact and head disk spacing control become more complicated in this experimental setup because the local heating generates a protrusion on the media surface. In this paper, we demonstrate a method to enhance the contact detection sensitivity significantly by modulating the head disk spacing. It shows that a light contact between the head TFC protrusion and media protrusion can be effectively detected. Thereafter, the media protrusion can be measured and the head disk spacing can be well set.

The microelectronics industry is pushing the fundamental limit on the physical size of individual elements to produce faster and more powerful integrated chips. These chips have nanoscale features that dissipate power resulting in nanoscale hotspots leading to device failures. To understand the reliability impact of the hotspots, the device needs to be tested under the actual operating conditions. Therefore, the development of high-resolution thermometry techniques is required to understand the heat dissipation processes during the device operation. Recently, several thermometry techniques have been proposed,such as radiation thermometry, thermocouple based contact thermometry, scanning thermal microscopy (SThM), scanning transmission electron microscopy (STEM) and transition based threshold thermometers. However, most of these techniques have limitations including the need for extensive calibration, perturbation of the actual device temperature, low throughput, and the use of ultra-high vacuum. Here, we present a facile technique, which uses a thin film contact thermometer based on the phase change material Ge2Sb2Te5, to precisely map thermal contours from the nanoscale to the microscale. Ge2Sb2Te5 undergoes a crystalline transition at Tg with large changes in its electric conductivity, optical reflectivity and density. Using this approach, we map the surface temperature of a nanowire and an embedded micro-heater on the same chip where the scales of the temperature contours differ by three orders of magnitude. The spatial resolution can be as high as 20 nanometers thanks to the continuous nature of the thin film.

In heat-assisted magnetic recording (HAMR), optical power from a laser diode mounted on the slider is used to heat up a nanometer scale area on the disk surface to approximately 450°C, facilitating the writing process. Controlling optical power or current that is applied to the laser diode in HAMR is a critical task. In this study, a fully integrated system of HAMR heads and disks is used to study laser current as a function of the magnetic write width (MWW), the operating radius, and the head-disk clearance. Our experimental results show that the laser current is a linear function of the magnetic write width and the head-disk clearance. As the operating radius increases from the inner diameter to the outer diameter of the disk, the laser current increases by approximately 20%.

The spacing between the flying head and the rapidly rotating disk in hard disk drives continues to decrease in order to grow the areal density. In heat-assisted magnetic recording (HAMR), the spacing control complexity is compounded by the additional protrusion resulting from the laser heating. Compared to the writer induced and thermal fly-height control protrusion, the near-field transducer (NFT) protrusion is a faster and more local protrusion that requires new HAMR-specific spacing control techniques. In this paper, we will review the simulation and experimental studies which shed light on both the steady-state and transient characteristics of the NFT protrusion. Simulation analysis reveals the scale of the protrusion and its effects on spacing control. Experimentally, we have demonstrated a novel technique to characterize the NFT protrusion and assist in setting the spacing for each HAMR head. Based upon the knowledge gleaned from characterization, compensation schemes have been developed. Some of the schemes have already been successfully demonstrated.

Contact hysteresis between sliding interfaces is a widely observed phenomenon from macro- to nanoscale sliding interfaces. Most such studies are done using an atomic force microscope (AFM) where the sliding speed is a few μm/s. Here, we present a unique study on stiction between the head-disk interface of commercially available hard disk drives, wherein the vertical clearance between the head and the disk is of the same order as in various AFM-based fundamental studies but with a sliding speed that is nearly 6 orders of magnitude higher. We demonstrate that, although the electrostatic force (dc or ac voltage) is an attractive force, the ac-voltage-induced out-of-plane oscillation of the head with respect to the disk is able to completely suppress the contact hysteresis.

Heat assisted magnetic recording (HAMR) has the potential to deliver higher storage areal density beyond 1 Tb/in2. A laser is integrated in the flying read/write head to heat up the magnetic media using a near field transducer (NFT). A large portion of the laser energy is absorbed inside the head, resulting in elevated temperature around the NFT. Thermal protrusions of different magnitudes and time scales occur after turning on the laser. These laser heating-induced protrusions must be characterized for each head and compensated in HAMR drives. In this paper, a magnetic recording-based method is proposed to perform in situ protrusion measurements and assist in setting the write spacing. This method has been successfully demonstrated on the spinstand and implemented into HAMR drives.

Heat-assisted magnetic recording (HAMR) promises to deliver higher storage areal density than the current perpendicular magnetic recording product. A laser is introduced to the HAMR system to heat magnetic media to reduce the media coercivity. The thermal response of the media becomes very critical for the success of the magnetic writing process. The study of thermal response time in HAMR relies on the setup configurations, such as laser spot sizes, the way that laser energy is delivered to media and the media structures. In this paper, the thermal response time of HAMR media under three different heating methods is systematically investigated through experiments and numerical analysis. A lumped model is built to simplify the heat conduction problem to understand the difference in thermal responses under various experimental conditions. Dominant layers are identified under those experimental conditions. The transient thermal response is mainly determined by the dominant layers. Engineering the dominant layers helps the most in optimizing the thermal performance of the media. Our study clearly suggests that for HAMR systems, optimizing the thermal properties of the heat sink layer is the key to reducing variations in the transient thermal process resulting from changes in the linear speed.

Resonance based enhanced contact detection is investigated at high sliding head-disk interface of hard disk drives. Acoustic signal arising from the contact in between the head and the disk is dominated by the resonance of the head air bearing frequencies. We show that modulation the head at resonance during the contact enhances greatly the acoustic signal generated during the contact between the head and the disk. As an application for HAMR HDDs, we used this scheme to detect the contact in between the near field transducer (NFT) and the disk which so far has been elusive

Heat assisted magnetic recording (HAMR) promises to deliver higher storage areal density than the current perpendicular magnetic recording products. Laser heating is implemented in HAMR to achieve magnetic writing of the very high coercivity media. However, the high temperature environment creates several reliability challenges for the head disk interface (HDI). In this paper, material transfer within the HDI under HAMR recording conditions is studied. The mechanisms of material transfer are explored via experiments and modeling. This study revealed that temperature difference and mechanical interaction between the head and media are the main mechanisms for material transfer inside the HDI. Possible methods to remove the material are also discussed in this paper.

We present a unique study on contact hysteresis between the head disk interface of the commercially available hard disk drives. We demonstrate that although electrostatic force (DC or AC voltage) is an attractive force, AC voltage induced out-of-plane oscillation of the head respect to disk is able to suppress completely the contact hysteresis.

Heat-assisted magnetic recording (HAMR) uses a laser to heat the magnetic media above its Curie temperature to enable magnetic writing when the write field is limited. However, there are thermal transients caused by the thermal–mechanical response of the head and media when HAMR writing starts. Understanding this transient and compensating for it are critical to successfully implement the HAMR system. In this letter, some possible contributions to the write start transient are discussed. Methods are demonstrated for achieving more uniform recording.

Heat transfer at nanometer scale attracts a lot of interest from both academia and industries. The hard disk drive (HDD) industry cares about the heat transfer between the head and disk, as several heating and thermal sensing elements are integrated into the HDD system. Understanding the heat transfer mechanism and its dependency on spacing becomes very critical for heat assisted magnetic recording (HAMR). In this paper, we propose a new method to study the head disk spacing effects on heat transfer by introducing a small perturbation to the spacing while maintaining the heating source unchanged. The dependency of heat transfer on the nanoscale spacing provides insights to the understanding of heat transfer mechanisms inside the nanoscale gap.