ENGINEERING FEATURE

If the Cap Fits - High Cap and Super Cap Technologies

Capacitors have been critical components in electronics applications since the industry began. But longevity doesn’t mean that pace of development has slowed – indeed, if anything, the rate of capacitor evolution is speeding up. And among the most exciting developments are multilayer ceramic capacitors that offer tantalum alternatives for certain applications, and ‘supercapacitors’ that deliver high pulse power and improve efficiencies in battery circuits. Here, we provide an overview of these latest capacitor technologies using examples from Arrow franchises AVX, Cooper Bussmann, Kemet, Murata, NEC Tokin, and Panasonic.

Pressures to improve system performance while increasing component density and reducing product size are fuelling the development of capacitor technologies with ever-higher Capacitance Value (CV) ratings in ever-smaller form factors. At the forefront of these developments are MultiLayer Ceramic Capacitors (MLCCs) that, in the last three years, have seen five- to six-fold increases in capacitance for a given size. Indeed, in a paper published last year by Murata, it was stated that ‘ceramic capacitors have been coming down in size and going up in capacitance at a speed that is comparable to Moore’s Law for the semiconductor industry’.

This is great news for the design engineer, as it means that ceramic capacitors are increasingly offering alternatives in applications demanding values of 1µF and above where, previously, say a tantalum or aluminium electrolytic device may have been the only alternatives. That is not to say that ceramics are about to completely replace tantalums or electrolytics, but it is clear that certain applications including decoupling and power supply filtering will now benefit from employing the latest MLCC technology. And, depending on operating frequency, in those applications where an MLCC is viable, engineers will derive further benefits from the proven reliability of MLCC technology and the fact that the lower ESR of the MLCC structure allows them to employ devices with smaller capacitance ratings than the tantalum alternative (see Table 1).

Capacitance Values

Tantalum Capacitor Value (µF)	Value of Possible MLCC Alternative (µF)
1	0.1 to 0.47
2.2	0.22 to 1
4.7	0.47 to 2.2
10	1 to 4.7
22	2.2 to 10
47	4.7 to 22
100	10 to 47
220	22 to 100

Table 1 - Replacing Tantalums – Typical MLCC Capacitance Values

Examples of ‘Hi-Cap’ MLCCs

‘Hi-Cap’ solutions are finding their way into cost-effective array products. Murata, for instance, is a pioneer of high CV MLCCs with its popular GRM range of devices as summarised in Figure 1.


Figure 1 – Murata GRM Line-up

Now, however, Murata has also launched a number of capacitor array products specifically aimed at designers seeking to meet tough cost and form factor constraints while maintaining product quality and further reducing PCB real estate. The company's Hi-Cap range of array products is particularly cost effective for applications requiring capacitances above 1μF. Whereas space saving is achieved by incorporating two or four elements in a single package, cost savings are accrued through lower purchase prices as well as reduced inventory costs and assembly effort.

In the popular 0504 package size, Murata offers two-element devices operating at 1μF, 10V and 1μF, 16V. In the 0805 footprint are a two-element 2.2μF, 10V part and a four-element 1μF, 10V device. A two-element 2.2μF, 6.3V part is available with a 0504 footprint, while two-element 4.7μF, 6.3V and 2.2μF, 16V devices are offered in 0805 packages. For applications requiring an extra low profile (0.7mm), Murata is releasing a two-element 1μF, 10V/16V (0504) part, and two-element 1μF, 16V (0805) array.

In addition, Arrow franchise AVX has responded to demands for high CV rating devices by producing an extensive range of medium-to-low voltage capacitors that address component count and board space-saving concerns. In particular, AVX’s high capacitance ceramic MLCCs (Figure 2) allow the use of smaller components with much larger capacitance values for power applications.


Figure 2 - AVX HiCV MLCCs

AVX has developed the HiCV MLCC output capacitor family to support the design trend of smaller capacitors with higher capacitance values, and the company believes that use of advanced manufacturing technologies to produce thinner dielectric layers, together with enhancements to material performance, will continue to drive this development. The HiCV MLCC output capacitors feature a base metal electrode system and an extensive voltage range of 4V to 35V. Low ESR values and high reliability, with low inductance, make the capacitor ideal for use as an output filter. HiCV MLCC output capacitors can also be widely used in decoupling applications. Chip sizes range from 0.60mm (±0.03) by 0.30mm (±0.03) with a thickness of 0.30mm (±0.03) to the largest chip size of 4.5mm (±0.03) by 3.2mm (±0.02) and a thickness of 2.79mm (±0.03). The capacitor series has a maximum operating temperature of +85°C.

Kemet is another company establishing a reputation for leading-edge ceramic capacitors with its own HiCV MLCC family, based on X5R and X7R dielectrics. In the last 12 months, for example, the company has announced significant extensions to this range, including the introduction of voltage extensions in EIA 0603, 0805 and 1206 case sizes. The company’s latest extended capacitance value offerings include:

• 12 new 0603-X5R parts, from 1.2µf to 2.2µf at 6.3V and from 0.27µf to 1µf at 16V
• Four new 0603-X7R parts, from 56μf to 100μf at 50V
• 12 new 0805-X5R parts, from 1.2µf to 4.7µf at 16V and from 0.47µf to 1.0µf at 25V
• Three new 1206-X5R parts, from 6.8µf to 10µf at 16V
• Three new 1210-X5R parts, from 12µf to 22µf at 16V

The operating temperature range of these capacitors is between -55ºC and +85ºC for the X5R MLCC and between -55ºC and +125ºC for the X7R MLCC, with zero bias capacitance shift limited to ±15% over those ranges. All parts incorporate Kemet’s standard barrier layer of pure nickel with an overplate of pure tin to provide excellent solderability as well as resistance to leaching.

Table 2 provides an overview of the latest and planned Kemet HiCV parts.

Maximum Available Capacitance by Dielectric and Voltage Rating

Case Size EIA	Case Size Metric	X5R 85°C 6.3V	X5R 85°C 10V	X7R 125°C 10V	X7R 125°C 16V	X7R 125°C 25V
0201	0603	0.1µF	0.022µF
0402	1005	2.2µF	0.1µF 1.0µF	0.1µF 0.22µF	0.1µF	0.047µF
0603	1608	10µF	2.2µF 4.7µF	1µF	1µF	0.22µF
0805	2012	22µF	10µF 22µF	2.2µF 4.7µF	2.2µF 4.7µF	1µF
1206	3216	47µF 100µF	22µF 47µF	10µF 22µF	10µF	4.7µF
1210	3225	100µF	22µF 47µF	10µF 47µF	10µF 22µF	4.7µF 10µF

Table 2 – Kemet HiCV Capacitors

Is it a Bird, is it a Plane? No, it’s Super Capacitor

Originally developed for military applications such as battery replacement on missiles and the starting engines of tanks, Supercapacitors (also referred to as Ultra Capacitors, Electrochemical Capacitors or Double Layer Capacitors) have, in recent years, become recognised for providing an excellent compromise between conventional capacitors and battery technologies. As a result, these capacitors, which are characterised by a low energy density and a very high power density, are being used in a broad range of pulse and non-battery reserve power source designs in applications ranging from ocean-going vessels to vehicles and mobile products.

Supercapacitor technology uses the ‘electric double layer’ phenomenon, whereby electricity is stored when a solid and liquid come into contact. Specifically, the supercapacitor structure comprises two electrodes separated by a semi-permeable membrane and placed in an electrolyte solution.

Panasonic is involved in the supercapacitor market, with its own range of surface mount electric double layer capacitors designed to provide engineers with an alternative to conventional battery back-up. Last year, for instance, the company began mass production of what is believed to be the industry’s smallest supercapacitor devices.


Figure 3 - Panasonic EP Series

Featuring diameters of just 3.8mm and heights of only 1.1mm, the EP series is ideal for small mobile electronics devices where the capacitors are able to address memory back-up requirements including power continuity during battery replacement.

In addition to the EP series, Arrow is also offering a Panasonic family of electric double-layered capacitors, known as 'Gold Capacitors'. Ideally suited for applications requiring a secondary power source, such as backup energy for microprocessors and energy storage for chargers or solar batteries, the main advantages of these products versus a battery are:

• Quick charge and discharge
• No charge and discharge cycle limitation
• Green product (RoHS compliant, no hazardous substances used, like lead or cadnium)
• No cycle restriction
• No charging protection circuit needed, easy circuit design
• Maintenance free and a very long life

NEC developed the first supercapacitors over 20 years ago and now, Arrow franchise NEC Tokin is one of the world’s leading suppliers of this technology. The company has developed a wide range of options for applications ranging from assistance for peak current demand to power back-up for primary power outages. Figure 4 illustrates how the company’s comprehensive product range spans a variety of application requirements ranging from the supply of short duration, high current power pulses that can assist with peak current demands, to long-term power back-up.


Figure 4 - NEC Tokin Supercapacitor Line-up

Among the latest developments in the NEC Tokin range is the HP series of ‘thin type’ low ESR supercapacitors. Developed to provide assistance for peak current demand in mobile devices, these supercapacitors have dimensions as low as 12mm x 2.0mm x 2.0mm yet are capable of current discharge in the order of amperes.

Cooper Bussmann is another company that has been pushing forward the boundaries of supercapacitor development with its PowerStor family (see Table 3).

PowerStor Aerogel capacitors are ultra-high capacitance devices based on a novel type of carbon foam known as carbon aerogel. The recent addition of the B series to the original A series fulfils a wide variety of new application and engineering needs. The B series are ultra-high capacitance cylindrical super-capacitors designed to complement the original A series ultra-low ESR supercapacitors. The B series has three times the capacitance of the A series by volume but only two times the ESR. Capacitance values range from 1F up to 50F. This combination of ultra-high capacitance and very low ESR makes the B series extremely versatile.

The PowerStor F series, on the other hand, is a flat-pack Aerogel Capacitor using similar packaging material and technique as Lithium ion polymer batteries. Replacing steel multi-layer foil-polymer packaging results in thinner, lighter cans with this new supercapacitor. The F series flat-pack Aerogel Capacitors can be designed for space constrained applications that require either an ultra-low impedance or high energy density.

Features, Benefits and Performance Characteristics

	A series	B series	P series	F series
Key Features	Ultra-low ESR (Resistance)	High energy density	Higher voltage	Polymer-foil laminate packaging
Key Benefits	Very high pulse power capability	Long run-time capability	Designed for 5V applications	Fit into space constrained applications as thin as 2mm
Capacitance	0.47F - 4.4F	0.22F - 50F	0.1F - 1F	0.33F
ESR	0.025Ω to 0.150Ω	0.025Ω to 3Ω	As low as 0.2Ω	0.250Ω
Voltage (Nominal)	2.5V	2.5V	5V	3.6V
Temperature	-25°C - 70°C	-25°C - 70°C	-25°C - 70°C	-20°C - 60°C

Table 3 - Cooper PowerStor Range

The AVX supercapacitor offering is based on the company’s BestCap ultra-low ESR supercapacitors. These devices provide excellent high power pulse characteristics in addition to extremely low leakage current.


Figure 5 - AVX BestCap

Based on a unique patented aqueous chemistry and innovative design, this series offers high capacitance, even with the short pulse applications found in GSM, GPRS, Edge and PCS telecommunications systems. And while BestCap technology offers more efficient energy savings in battery circuits than many conventional supercapacitors, its low ESR results in a high current handling capability which is ideally suited to portable or wireless devices requiring high power availability. Finally, low profile versions are well matched to the needs of PCMCIA, PDA, DSC and similar applications.

A Note on Batteries

It is worth concluding by pointing out that, despite the incredible advances being made in supercapacitor technologies, designers of portable equipment still need to identify and select suitable battery technologies for their applications.

Fortunately, Arrow can also help here, thanks to a broad range of primary, rechargeable and button cell technologies. The Panasonic range from Arrow, for instance, offers a comprehensive choice of cylindrical and prismatic Li-ion and NiMH solutions, in addition to cylinder type, coin type and rechargeable button cells.


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