Power system designers are constantly under pressure to attain larger power densities and improved conversion efficiencies, whether it is for data servers for the internet of things or data centers. Although semiconductor switching devices have received a lot of attention to make these advances, capacitors may also be a significant design component in helping engineers satisfy energy storage, filtering, leveling, and tuning needs.
However, capacitor development has not kept pace with changes seen in the semiconductor world and even leading technologies such as multilayer ceramic capacitors (MLCCs). MLCCs are monolithic electronics made up of layers of metal electrodes and ceramic dielectrics that alternate. High temperatures are used during the fabrication of the laminated layers of MLCCs to create a sintered, volumetrically effective capacitive device. A conductive termination barrier is then incorporated at the exposed ends to complete the connection.
Empower Semiconductor (Empower) developed its own 220-nF capacitor technology (E-CAP) to complement its series of integrated voltage regulators (IVRs) after recognizing the drawbacks of traditional capacitors. In an interview with Power Electronics News, Steve Shultis, senior vice president of sales and marketing at Empower, discussed how the advantages of E-CAP have allowed the firm to profit from advancements in IVR systems. “E-CAP combines a variety of discrete capacitances into one solid-state component,” he said. “In order to take advantage of their superior performance, size, configurability, durability, and stability, Empower now provides E-CAP silicon capacitor solutions in a number of difficult application areas.
“We spent a lot of time realizing that even the highest-performance ceramic capacitors would not be able to sustain our 100-MHz or 200-MHz switching frequency for the first generation of IVRs when we were developing the initial IVR platform four years ago,” he added. “We thus realized that we needed something new, and together with our partner TSMC, we found a technique that utilized this technology and became specialists in designing for it. We are moving it in a path that, like IVR, involves power management and was not previously considered.”
Empower revealed that its partner is TSMC, with whom there is collaboration in implementing E-CAP. “The intellectual property of the design is ours, but through TSMC, you can use their process, so you can take the intellectual property and apply it to another process,” said Shultis.
Last week, Empower Semiconductor announced that it has expanded its E-CAP family of silicon capacitors with new technologies that offer further breakthroughs in density and performance. The latest E-CAP solutions offer densities of 1.1 µF/mm2. In addition to the density, thickness levels can be achieved below 50 µm in overall height. Multiple, matched capacitance values from 75 pF to 5 µF (at 2 V) can be integrated into a single die to create custom integrated capacitor arrays. Packaging options based on bumps, pads, and pillars allow designers to choose the best solution based on specific system constraints (Figures 1 and 2).
Figure 1: ECAP-based solution provides >5× density compared with standard MLCCs. (Source: Empower Semiconductor)
E-CAP integrates multiple capacitors into a single solid-state device, offering the flexibility and efficiency of silicon. According to Shultis, the technique combines an enhanced equivalent series inductance (ESL) and equivalent series resistance (ESR) characteristic that significantly lowers parasitics with a capacitor density that is nearly 5× greater than that of leading MLCCs.
Shultis emphasized the ability of E-CAP technology to achieve thickness levels of less than 50 µm, which is perfect for supporting next-generation data-intensive systems that demand high-frequency operation and maximum efficiency from the smallest form factors, as well as in the IoT, wearables, mobile, and processor sectors, where size, performance, and flexibility are crucial. E-CAP solutions help designers lower the cost of the BoM and the risk of circuitry failure.
“With more capacitors integrated into a given area, you can put a lot more capacitors into a smaller area, giving you flexibility for a range of common applications below 4 V,” said Shultis. “High-voltage work necessitates specialized processing with tradeoffs. Empower is scouting the landscape for potential new prospects.”
Figure 2: E-CAP vs. MLCC (Source: Empower Semiconductor)
Figure 3: Example design replaces 10 MLCCs with one E-CAP die; single-die solution for nine-capacitor requirement for ultra-high–density application. (Source: Empower Semiconductor)
Additionally, unlike MLCCs, which require several devices to account for de-rating from voltage, temperature, and age, E-CAP has minimal or no requirements for AC or DC bias de-rating. As a result, there is no longer a need to “over-spec” capacitance needs to take de-rating into consideration.
“Calculations are needed to determine the appropriate temperature, voltage, DC rating, etc. while using MLCCs,” said Shultis. “Due to low de-rating from voltage, temperature, and age, E-CAP does not need overdesign. To demonstrate this, we may cite our outstanding performance in terms of qualification, dependability, and client production. The ESL is the other non-negligible component, which is why high-performance decoupling systems often employ it, as only a small amount of inductance is required and is provided by the capacitor throughout the whole line. There are ceramic capacitors with low inductance, but they normally cannot achieve single-digit picohenry values and are more costly, as they are made of highly customized and specialized ceramics.”
Figure 4: Empower E-CAP design examples (Source: Empower Semiconductor)
Figure 5: MLCC construction vs. silicon trench capacitor (Source: Empower Semiconductor)
Flexible capacitors with an ultra-low ESL of as little as 15 pH and a package height of 50 µm are available through E-CAP for use in mobile and wearable devices to data center servers and IoT devices. E-CAP has a lower impedance at high frequencies due to its better frequency response and stronger ESL. Figure 3 contrasts two implementations: one that employs E-CAP in place of high-frequency capacitors and one that uses numerous MLCC capacitors to increase the frequency responsiveness of a decoupling solution. According to the results, Figure 3 shows that the number of components can be reduced by 40% through the use of E-CAP while simultaneously lowering the impedance at high frequencies to half that achieved with the traditional MLCC-based solution.
“According to Figure 4, our roadmap is meant to offer a variety of options; however, as we speak with more and more customers and applications, we understand that a sizable percentage of the market has a general requirement for 200 nF or 400 nF,” said Shultis. “We have already put a few second-generation multicap-type designs into practice. The one with 18 capacitors is most likely to become a regular item: 18 200-nF capacitors are included in the easily accessible product, although the array is roughly 2 × 2 mm, has a 400-µ pitch, and has a total capacitance of about 4.8 µF. Thus, it may be used in the majority of PCB-mounting situations. The second generation can go below 50 µ in thickness. The very small decoupling capacitors on the underside of the substrate are so thin that they can fit within the height limits, even for mounting after soldering or inside substrates or PCB layers, so we are working on these packaging technologies and how this can be done.”
Shultis asserted that E-CAP capacitors are secure for usage in magnetic field conditions and resistant to low-frequency noise (Figure 5). “This is a challenge for some low-frequency applications using MLCC ceramic capacitors,” he said. “We have run into this issue on a few occasions. Additionally, nickel plating on the pads of ceramic capacitors makes them troublesome for use in medical applications, as it is magnetic-field–sensitive.”
>> This article was originally published on our sister site, Power Electronics News.
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