New dimensions in integration and miniaturization
Smartphones need more than ever – but smaller than ever
With the ongoing and strong demand for smartphones to pack more features into a small form factor, TDK Corporation is successfully leveraging the strengths of both TDK’s and EPCOS' technologies to achieve new dimensions in miniaturization and integration and offer compact products with extremely low insertion heights.
The technological breakthroughs for TDK and EPCOS products span the whole range of functions for smartphones from the audio right the way through to the RF sections plus EMC protection. The company offers a whole raft of technologies and products to enable the designer to produce the highest value performance demanded in this particularly competitive business arena spanning high integration, new materials and innovative packaging. In addition, TDK offers solutions based on thin-film and MEMS technologies.
The next mobile radio generation LTE (Long-Term Evolution), smartphones must support even more frequency bands in addition to bands for existing 2G and 3G networks, driving the need for additional miniaturized components; (SAW filters, duplexers, power amplifiers etc.). Smartphone manufacturers must integrate functions and construction elements without influencing the size and importantly, the thickness of the phone. Against this background, the insertion height of miniaturized components has become one of the decisive challenges in creating competitive components.
DSSP technology: A new dimension in miniaturization
The innovative die-sized SAW packaging technology DSSP® from EPCOS represents a major milestone in the miniaturization of discrete components. For the first time, component sizes are identical with the chip size, thus offering the highest degree of miniaturization currently available in the market.
Filters and duplexers in DSSP technology are designed primarily for use in RF modules, as these require the highest degree of miniaturization both in terms of surface area and insertion height. With an insertion height of just 0.25 mm, DSSP components are significantly flatter – 40 percent – than products manufactured in currently available CSSP3 packaging technology. The footprint of DSSP components is also up to 85 percent smaller than that of first generation CSSP® products (Figure 1).
With a fine pitch of only 220 µm the DSSP technology takes full advantage of the state-of-the-art in module manufacturing. During the module production process, DSSP products can withstand molding at pressures of up to 80 bar and are tested according to IPC/JEDEC J-STD-020B MSL2a. DSSP components consist of a filter wafer and a cap wafer made of the same material (lithium tantalate or niobate). Both wafers are bonded at wafer level. The mass production of first DSSP products has already begun and the product portfolio of RF duplexers and filters for LTE/WCDMA, GSM, and navigation systems is being extended.
DSSP duplexers will be mainly used for integration in FEMiDs (front-end modules with integrated duplexers), duplexer banks and PAiDs (power amplifier modules with integrated duplexers). EPCOS DSSP duplexers offer not only best-in-class performance, but also a smaller footprint and significant savings in insertion height. The typical surface area of the first DSSP duplexers will be 1.8 x 1.4 mm² with an insertion height of 0.25 mm. Customer samples are already available for duplexers for W-CDMA bands V, VIII, XIII and XVII.
The DSSP filter portfolio can be divided into two categories: cellular RF filters for GSM systems, for example, and filters for navigation systems. GSM filters are offered either as single filters or as single-chip 2-in-1 filters. The application for GSM filters in DSSP technology is very similar to that of duplexers, and they can be used to miniaturize any RF front-end module.
SESUB technology for ultra flat modules
Certainly, one of the key trends in miniaturization is to combine many functions and components into self-contained modules or systems in package (SIP). In this context, TDK has launched SESUB (Semiconductor Embedding Substrate), an innovation that offers significant miniaturization potential and, together with the company’s 3-D RF design expertise, will significantly drive the miniaturization of complete RF front-end solutions for mobile phones, for example.
SESUB not only enables the embedding of passive electronic components directly into the substrate layers, but also that of highly integrated ASIC and controller dies with a thickness of around 50 µm and with a large number of fine-pitch I/Os. This results in extremely flat and space-saving modules (Figure 2). One of SESUB’s key benefits is that it also acts as a redistribution layer to the PCB. Components that cannot be integrated into the substrate are mounted on top of the substrate stack. In this way, modules and SIPs can be implemented with considerably smaller dimensions with insertion height reduced by around 35 percent, e.g. from 1.55 mm to no more than 1.0 mm. This is made possible by an extremely thin substrate layer stack with a total height of only 300 μm and micro-interconnection structures and vias.
Especially smartphones integrate many functions, e.g. WLAN, Bluetooth, GPS, NFC (near field communication), mobile TV, and the requirement for miniaturized components becomes crucial in relation to size and cost.
|Figure 2: Space saving SESUB modules|
The compact construction of SESUB delivers excellent thermal attributes due to the use of copper end terminals, higher performance EMC and high reliability. Especially, this superior thermal performance is important for applications in the area of power management, transceivers, processors, and the power amplifier (PA). A comparison between discrete-packaged power semiconductor chips with a SESUB-embedded solution, results in around 7 K lower chip surface temperature. The industry-leading thermal performance achieved in SESUB delivers significant advantages in the design of power semiconductor chips.
The new module architecture relieves manufacturers of mobile phones from time-intensive design work to an even greater degree. In addition, the logistics outlay is reduced, as only a single module is needed instead of numerous discrete components.
SESUB is well suited as a new integration platform, and not only for RF modules. It also allows optimally miniaturized power management modules and DC-DC converters.
Advanced thin-film technology for even lower profile components
In order to create electronic components with even lower insertion heights TDK has adopted its leading-edge thin-film technology which has proven itself in the manufacture of magnetic heads for hard disk drives. This technology enables the successful combination of outstanding performance characteristics with the smallest dimensions and a low-profile form factor, making such products ideal for smartphones.
A good example is the TDK MLG 0402 and 0603 series of multilayer chip inductors with high Q values. Because a huge number of components must be tightly packed on the circuit boards, multilayer chip inductors using thin sheets made of ferrite or other materials must become even smaller and feature an extremely low profile. To realize high Q values, high-precision manufacturing techniques are required that minimize distributed capacitance and skin-effect while enabling optimized design of internal electrodes which is the key to realizing compact dimensions in a smartphone design project.
Filtering and protection are vital to the stability and protection of smartphone designs. The TDK TCE1210 series is the first thin-film common-mode filter to offer both high-speed common-mode noise suppression and ESD protection in a single component (Figure 3).
|Figure 3: Thin-film common-mode filter with integrated ESD protection|
Thin-film micro-wiring technology also enables RF components to be slimmed down. The new TDK TFSB series of thin-film band pass filters offer a footprint of 1.0 x 0.5 mm² and an insertion height of just 0.3 mm. The filters are designed for the 2.4 GHz and 5 GHz bands, making them suitable for Bluetooth and WLAN applications in smartphones and other mobile phones.
The company’s comprehensive range of products for smartphones also include ceramic transient voltage suppressors (CTVS) for the ESD protection of data, audio and video lines. The portfolio comprises different series of multilayer varistors as well CeraDiodes®. All devices are bidirectional devices. By contrast to TVS diodes they route both positive and negative ESD transitions safely to the ground plane. This technique eliminates the need to route ESD charge into the power plane, which could damage nearby ICs.
The newest developed CTVS “low clamping voltage series for portable devices” fits well to the today’s requirements of smartphone applications. This series offers excellent clamping capability, low leakage current, fast response time and high robustness in miniaturized packaging (EIA 01005 & 0201).
Multilayer ceramic capacitors (MLCCs) combine miniature size with larger capacity. They are used to reduce noise and set circuit constants, and are found in almost all electronic equipment. Primary applications are noise suppression and assisting power supply. The former function is possible due to the low impedance values of MLCCs in high-frequency ranges. High-frequency power supply noise generated in the IC is bypassed to the ground layer. This limits high frequency power supply noise to the immediate IC region, preventing it from escaping into the board. The quantity of MLCCs in smartphones has increased as functions become increasingly sophisticated.
MEMS technology for smartphones
Smartphone users demand increased functionality and an improved user experience from their devices. MEMS (micro electro-mechanical systems) enable a vast number of applications from audio, gesture recognition to navigation, while improving the power efficiency and robustness of electronic devices.
Based on EPCOS design capability for cutting-edge MEMS and ASIC technology, deep application know-how and a strong patent portfolio, the first products to be introduced were the EPCOS T4000 and T4010 microphone series, followed by the T4030 series of digital output microphones and the T4060 series of analog output microphones. Thanks to their compact dimensions and outstanding electrical properties the microphones are predestined for applications with high requirements for audio quality.
All types of EPCOS MEMS microphones are manufactured in the CSMP™ (chip-sized MEMS package) technology, which was developed for SAW filters and has already proved itself in billions of mobile phones (Figure 4). Customers can benefit from mature EPCOS production processes as well as more than 15 years experience in the development of MEMS microphones.
|Figure 4: Robust packaging for MEMS microphones|
The C914 MEMS microphone, one of the newest members of the leading-edge microphone product line, features a very high signal-to-noise-ratio (SNR) of 65 dB(A), making it particularly useful for high-end audio applications in smartphones. The high SNR and very low total harmonic distortion (THD) improves audio quality significantly when recording distant sound sources.
The new C920 and C923 MEMS microphones are two of the smallest top-port microphones in the market and employ a unique packaging approach which practically eliminates resonance problems and provides a flat frequency response up to the limit of the audible spectrum. The C923 has a flat frequency response down to the lower limit of the audible spectrum while the C920 features a high-pass filter that filters out low frequencies below 100 Hz which helps to block wind noise.
Miniaturized pressure sensors can also be integrated into smartphones. With dimensions of only 2.2 x 2.8 x 0.7 mm³, the calibrated and temperature-compensated EPCOS T5400 digital pressure sensor is one of the world’s most compact packaged sensor. Designed for measuring absolute pressures from 300 to 1200 mbar, it provides a 16 bit resolution at the serial digital interface. It has a low power consumption of only 0.2 μA in sleep mode and <1 mA while operating. The T5400 requires no further calibration. This benefits developers of navigation equipment and mobile phones, for example, who wish to accurately determine altitude above sea level with the aid of air pressure measurements. Together with a GPS-determined location, the altitude measurement permits precise 3D positioning. Applications include navigation devices with 3D maps. Moreover, it also enables position information accurate to within a single story of a building for emergency calls from mobile phones.