TDK’s Environmental Technologies
(1) Thin-Film Technology for HDD Heads
Inside an HDD unit, the disk produces wind pressure as it rotates at high speeds. Buoyed by this wind pressure, the "swing arm," fitted with a magnetic head on its tip, flies approximately 2-3 nanometers above the disk, writing and reading data to and from the disk surface at high levels of speed and precision (Figures 1-3).
Figure 1: Internal construction of an HDD (Ex.)
Figure 2: A magnetic thin-film head in stable flight over a disk rotating at a high speed
Figure 3: Diagram of magnetic head and disk
The magnetic head, serving as the heart of the HDD, consists of a recording head that magnetically records data to the surface of the hard disk and a playback head that reads stored data. During the recording process, binary signals are written to the disk according to changes in the flux coming from the tip of the recording pole (Figure 5 on the next page). When a magnetic head reads stored data, the Giant Magnetic Resistivity (GMR) playback head detects magnetic signals on the surface of the disk and generates binary signals based on magnetic strength.
The coils, yokes, and GMR elements that make up these recording and playback heads are all formed by thin-film technology and controlled at thicknesses in the nanometer order. The GMR element houses layers such as an antiferromagnetic, a pin and a free layer. These layers are also measured in nanometers, making it a prime example of what nanotechnology can do.
Figure 4: Electron microscope photograph of a wafer during the head production process
Figure 5: Electron microscope photograph of a head cross-section
These nanotechnology-based thin-film magnetic heads are now capable of achieving recording densities of up to 750 Gbpsi. Thrust onward by ongoing technological advances, such as the heat assist method that uses a laser to heat the surface of the disk and thereby provide another boost to recording density, it is only a matter of time before these heads push past the 1-Tbpsi threshold. With TDK's cutting-edge thin-film head technology blazing the trail, the HDD units that people around the world depend on for personal computer storage will continue to charge forward on the evolutionary path.
The technology also has a positive environmental impact. As recording density goes up, so does per-unit HDD recording capacity; this not only reduces the number of disks required but also allows for smaller disk diameters, thereby saving natural resources. By making HDD units and, by extension, computers smaller, thinner, and lighter, the technology represents a significant improvement in resource effectiveness.
(2) The TCE Series: Thin-Film Common Mode Filters with Built-in ESD Suppression
Interface cables that connect smartphones, mobile phones, and other mobile devices to digital devices like computers are major gateways for radiated noise. As mobile devices continue to reach higher speeds and higher frequencies, common mode noise is becoming an increasingly important issue to address.
Using highly advanced thin-film processing technology, TDKs TCM series of thin-film common mode filters were developed. Thanks to its remarkably small and thin dimensions, it won a CHO MONODZUKURI Innovative Parts and Components Award 2008 in the Electronics and Electronic Components category (given by Nikkan Kogyo Shimbun, Ltd.).
TDK offers the ACM series (Figure 6), wire-wound filters with ferrite drum cores. However, in order to respond the need for smaller and lower-profile filters, the TCM series (Figure 7) is developed now. This series applies the advanced thin-film processing technologies, which the company originally developed through the production of HDD heads, to the lamination of thin-film conductor coils onto ferrite layers. The result was a thin-film common mode filter that takes up less than one-eighth the area and one-thirtieth the volume and weight of a conventional filter.
Figure 6: Structure of the ACM series
of winding-wire common mode filter
Figure 7: Structure (diagram) of the
TCM series of thin-film common mode filter
Meanwhile in interface terminals for electronic equipment, another type of EMC suppression is essential. It is electrostatic discharge (ESD) suppression, protecting circuits against ESD emitted from the human body. Actually ESD can reach several thousand volts, which may cause unprotected ICs to malfunction or suffer severe damage (Figure 8). With their cables being frequently plugged in and removed, mobile devices experience a considerable amount of touching and therefore require especially reliable protection. The TCE series combines a thin-film common mode filter with ESD protection elements to create single, integrated common mode noise suppressors.
Figure 8: The tip of a finger (top) charged to -5 kV and discharged onto a metallic ball
Although TDK mass-produces varistors for ESD protection, the TCE series uses micro-gap ESD suppressors (electrostatic discharge suppression elements) that are better suited to thin-film technology.
In this type of system, voltage is applied inside the micro-gap at gradually increasing levels. When the voltage reaches a certain point, a breakdown occurs in the gap, releasing static electricity. Taking advantage of its thin-film technology, the new TDK product successfully fits a micro-gap and a common mode filter inside a chip as small as 1.25 x 1.0 x 0.6 mm. As shown in Figure 9, the common mode filter portion includes an insulating layer situated between two opposing coil layers, while the ESD suppressor portion sandwiches a conducting layer and an ESD absorbent material layer, which together form the gap, between insulating layers. All of these components were created with thin-film fabrication methods. Figure 10 shows the exterior and equivalent circuit schematic of the TCE series common mode filters with built-in ESD suppression.
Figure 9: Structure of a common mode Filter
with built-in ESD suppression
Figure 10: Exterior and equivalent circuit
schematic of the TCE series
By combining a common mode filter and ESD protection elements to make dimensions smaller and thinner than ever before, the TCE series (1210 size) has earned its place in TDK's SUPER ECO LOVE lineup. We will continue to develop the TCM and TCE series, building around our thin-film common mode filter technology.
(3) Miniaturized Thin-Film RF Components
(3-1) The TFSB Series: Thin-Film Band Pass Filters
Smartphones and mobile phones use wireless communication technology in the GHz band, which operates at extremely high frequencies. In order to sift through the many signals flying around at different frequencies, these devices use a variety of band pass filters (BPF) that ignore unwanted signals and pick up only the necessary signals with a high degree of precision.
To cope with the superhigh frequencies involved, BPF in the GHz band are often created with unique materials and configurations. Examples include filters that use surface acoustic waves (SAW), filters that use blocks of dielectric material, and even filters in which multiple thin dielectric ceramic layers and conductor pattern layers are stacked on top of one another in an alternating fashion (Figure 11). Each type has its own unique characteristics and optimal applications, but the multilayer ceramic type is the most popular choice for the 2.4GHz frequency band used with Wi-Fi (wireless LAN) and Bluetooth technology.
Figure 11: Exteriors of TDK Wi-Fi BPF products (2.4 GHz band)
TDK has mass-produced large quantities of different multilayer ceramic BPF. Currently, the smallest available size of this type is 1.6 x 0.8 x 0.5 mm. With smartphones and mobile phones evolving into more sophisticated forms with each passing day, TDK has poured its energies into researching new applications of the thin-film technology it originally developed for HDD magnetic thin-film heads in order to meet the intensifying demand for smaller, thinner, and lighter high-frequency components. The company's efforts found fruition in thin-film BPF, whose internal structure consists of a capacitor and coil created via the thin-film process. At a size of only 1.0 x 0.5 x 0.3 mm, TDK's thin-film BPF achieves a 77% reduction in volume and weight compared to traditional multilayer ceramic BPF and still manages to maintain almost exactly the same frequency characteristics.
Figure 12: The TFSB series of thin-film BPF for Wi-Fi / Bluetooth
The position of the terminal electrode is another defining feature: unlike most conventional BPF, which have terminal electrodes on their side surfaces, the thin-film BPF has its terminal electrode on the bottom surface. This allows the soldered conductor pattern to fit within the BPF size during substrate mounting and consequently delivers an additional reduction in total mounting area. Given its abilities to make BPF significantly smaller, thinner, and lighter, the TFSB series of thin-film BPF (Figure 12) is one of TDK's SUPER ECO LOVE products. The new TFSB series products, designed for the 2.4 GHz and 5 GHz bands that cover all Wi-Fi systems, employ thin-film technology to achieve worldstandard BPF performance. Graph 1 illustrates BPF frequency characteristics in both bands.
Graph 1: Frequency Characteristics (Ex.) for the TFSB Series of Thin-Film BPF
(3-2) Z-match: Thin-Film Capacitors
Another major product of TDK's research on applications of its thin-film technology is Z-match, a thin-film capacitor for impedance matching often used in high-frequency circuits. Inter-element matching is crucial in minimizing energy loss caused by reflection and radiation when devices are connected electrically in a circuit using high-frequency signals in the GHz band. Most matching circuits use coils and capacitors for this purpose.
The most common matching capacitor is the multilayer ceramic capacitor (MLCC) type. TDK's newly developed thinfilm capacitor, however, goes a step further than conventional components. Despite having the same dimensions as the smallest MLCC (0.4 x 0.2 x 0.2 mm), the new technology maximizes the benefits of thin-film processing to deliver not only a vastly superior capacity value tolerance (±0.05 pF) than its MLCC counterpart, but also a high Q factor and dramatic improvements in self-resonant frequency. The product's withstanding voltage (16 V) is sufficient in practical applications, while its temperature characteristics boast stability in the C0H range. Like the TFSB series thin-film BPF, the thin-film capacitor is configured so that the terminal electrode is located on the bottom surface.
These innovations facilitate the design of high-frequency circuits, create additional space, and boost performance. Figure 13 shows the exterior of the Z-match thin-film capacitor, and Graph 2 provides an overview of the product's self-resonant frequency (SRF) properties (Z-match is a registered trademark of the TDK thin-film capacitor).
Figure 13: The Z-match of thin-film capacitor
Graph 2: The SRF characteristics for
the Z-match of thin-film capacitor
By utilizing and expanding the applications of the thin-film technology it first cultivated for magnetic thin-film heads, TDK has developed a selection of unique, innovative high-frequency parts. We are excited about venturing beyond thin-film BPF and capacitor products to create even more diverse, environmentally friendly thin-film, high-frequency products.
(4) TDK system for creation of Environment-Conscious Products
TDK implements very stringent rules for assessing a product's qualities already during development, taking environmental aspects into consideration right from the initial concept and through the various design stages. Construction and material selection are guided by environmental principles, and the entire life cycle of a product, from obtaining raw materials until disposal (parts procurement -> manufacturing -> distribution -> use -> disposal) is subject to a comprehensive evaluation system.
During this severe assessment process, new products that demonstrate a particularly beneficial and ongoing reduction of environmental impact, with the potential to play a leading role in the industry, are designated as SUPER ECO LOVE products or ECOLOVE products (Note 1).
Note 1: In order to promote awareness of SUPER ECO LOVE and ECO LOVE products also among consumers, TDK is endorsing the use of relevant symbols.
(Please refer to "Eco Love Products and the Eco Love Logos" in the "Environment-Conscious Products" section of our web site.)
The TDK Group will continue to develop and apply advanced technology with the aim of making a significant contribution to improved fuel economy and the conservation of natural resources, applicable not only in the EV/HEV sector but to all kinds of automobiles.