Changes in temperature requirements for defense and downhole drilling applications have challenged the capacitor industry to produce new components that can operate in exceptionally high temperatures for longer periods of time.
For decades, the operating temperature of competing high-temperature dielectric materials consumed in capacitor anodes was limited to about 200 C and available capacitance values were limited to the picofarad range. There was also the added problem of limited volumetric efficiency of the capacitors being offered for this demanding circuit environment.
The subsequent trend has been to increase the operating temperature of the capacitors competing in the space and to increase the capacitance range into microfarads, while also expanding product case size offerings, types of component configurations and the lifespan of the components themselves.
Multiple exotic dielectrics are employed to operate at elevated temperatures. These include exotic variations of ceramic, tantalum, plastic film, mica, solid aluminum, glass, silicon, diamond-like carbon and aluminum oxynitride. Ceramic, tantalum, plastic film, glass and diamond-like capacitors have established reliability in the ultra-high temperature arena above 170 C, while solid aluminum, silicon and aluminum oxynitride are emerging technologies that have market potential.
Because the end-markets into which these high temperature capacitors are sold include both defense and oil-and-gas related electronic subassemblies, these high temperature capacitors are usually subjected to additional rigors of extreme environments, such as enhanced vibration frequencies, high voltage environments and radiation exposure.
Subsequently, failure modes for these application-specific capacitor types are intense and include delamination, tombstoning, thermal stress cracking, tin whiskers (truly terrifying), dramatic “rollercoaster-like” fluctuations in capacitance with temperature, and questionable insulation resistance.
To summarize:
- There is increased market activity in the 175 degree C to 450 degree C capacitor markets because of the commercialization of space and the impact geothermal electronics.
- Established dielectrics operating at such high temperatures include ceramic, tantalum, plastic film, glass and diamond-like capacitors. [1]
- Capacitor manufacturers are also exploring new high temperature dielectrics, especially in “self-healing” plastic film, which is preferred in mission critical circuit applications.
- Emerging capacitor dielectrics operating at these temperatures include silicon, solid aluminum and aluminum oxynitride type capacitors.
Market Opportunities in High-Temperature Capacitors
The high-temperature capacitor market (i.e. for applications greater than 175 C) has been growing at a rate that exceeds traditional value growth in the capacitor industry since my firm, Paumanok Publications, first started covering this technically rewarding segment of the high-tech economy. This is the result of a large increase in demand from the aerospace and geothermal industries as a result of new civilian space projects and the additional of new geothermal tools.
The products driving most development and demand for high temperature dielectrics include downhole pump sensors, aircraft engine sensors and geothermal sensors. These capacitor-intensive subassemblies are subjected to the most demanding environments [2]:
Satellites: Power supply systems for communications and weather satellites
Aircraft: Transmitter power supplies for electronic countermeasures (ECM); starters for jet ignition systems; multiple power supply systems
Ships: Radar transmitters for shipboard defense systems
Weapons: Detonator devices for exploding foil initiators used in electronics safe and arm devices (ESADs); guidance system transmitters for missiles
Sensors: Partial discharge sensing equipment
Radar: Pulse forming network transmitters; travelling wave tube (TWT) power supplies for radar transmitters
Spacecraft (i.e. the International Space Station): multiple requirements that are related to power supply
Unpackaged Bread-boarding Circuitry
The largest of the commercial markets for is for downhole pump applications (mining and oil well electronics). Oil well drilling electronics (sensors, gages and monitors) typically operate in the 175 C to 200 C range, while mining operations that are exposed to gas, steam and geothermal environments can require components that operate from 225 to 300 degrees C or above. (Other product markets that have high heat operating environments include power generation equipment and large industrial turbine-mounted electronics.)
In many instances, the electronic systems involved in these extreme applications employ capacitors based upon reconstituted mica, metallized Teflon®, metallized PTFE or specialty glass capacitors. Single-layered and multilayered ceramic chip capacitors (stacked ceramic chips) are also used, and for higher capacitance applications the tantalum “wet slug” capacitor is used. However, these capacitors have much higher average unit selling prices when compared to the MLCC or molded tantalum chips traditionally used in more commercial applications, such as phones and tablet computers.
High-Temperature Capacitor Markets By Dielectric:
As noted above, the established dielectrics for high-temperature capacitors (>175 C) are ceramic, tantalum, plastic film, mica, glass and diamond-like carbon capacitors. Emerging dielectrics include silicon, solid aluminum electrolytic and aluminum oxynitride.
Ceramics – This includes all ceramic types and configurations including multilayered ceramic chip capacitors, multilayered axial and radial leaded ceramic capacitors, stacked capacitors and single-layered ceramic disc capacitors manufactured for high temperatures ( >175 C). These ceramic capacitors are primarily in X7R, NPO and X8R type dielectrics.
The supply of high-temperature ceramic capacitors for applications above 175 C is highly fragmented, with many of the smaller, more specialized vendors of ceramic capacitors offering a variation on the high temperature ceramic capacitor.
Tantalum – Certain types of tantalum capacitor designs are used in high temperature applications. These include tantalum wet slug capacitors and molded solid tantalum chip capacitors that are consumed primarily in defense and downhole pump applications. Tantalum wet slug capacitors are unique in their design and construction, and are very difficult to manufacture. They are consumed in high-temperature applications that require the added value of high capacitance.
Plastic Film – There is some surface-mount film capacitor “activity,” but it is very limited at the time of this writing and almost all configurations are axial-leaded and/or radial leaded designs. These plastic film capacitors compete effectively for board slots in high temperature applications with ceramic capacitors, and are made almost exclusively of Teflon® and Kapton® (PTFE, poly-tetrafluoroethylene) plastic films.
Plastic film capacitors have an advantage over ceramic capacitors in high-temperature applications because of the self-healing capabilities that are inherent to the plastic dielectric. However, ceramic has an advantage over the film dielectric because of its volumetric efficiency. Ceramic capacitors offer similar capacitance and voltage-handling capabilities in a smaller case size when compared to plastic film. Ceramic capacitors are also more profitable in high-temperature applications because of the lower cost per pound of their ceramic dielectric materials when compared to metallized Kapton® or Teflon®.
The supply of high temperature plastic film capacitors is extremely fragmented, with many of the smaller vendors that supply the defense market offering wound Teflon® and Kapton® plastic film capacitors. [3]
New developments in recent years have centered around high-temperature polyethylene (HTPE) and fluorene polyethylene (FPE) films.
Mica – Mica capacitors are a unique and specialized segment of the capacitor industry worldwide. The market is extremely small overall, but a major portion of the units sold are for high-temperature applications >175 degrees C. Made-to-order mica paper capacitors are available for a variety of high-temperature/high-voltage applications. In terms of capacitance voltage, mica paper capacitors also resemble the electrostatic performance characteristics of ceramic and plastic film capacitors. They have low capacitance values in the picofarad range to the low microfarad range and are available in high-voltage designs to 15 kV.
Glass – Glass capacitors are unique designs consumed almost entirely for defense markets. Glass capacitors are very difficult to manufacture and require a unique production process that utilizes a unique flexible glass substrate that can be rolled onto a mandrel to create a unique axial-leaded capacitor design.
Silicon – Silicon capacitors manufactured using the advanced sputtering process are a relatively new product on the market. The dielectric and production methods enable this chip design to be applicable for high temperature applications.
Diamond-Like Capacitors (DLC) – K Systems, Inc. offers a diamond-like capacitor which has been available for many years now. This technology was developed by K Systems under agreements with the United States Air Force. This product line is also suitable for >175 C applications. It remains a small and custom type market.
Aluminum Oxynitride – K Systems, Inc. has also developed high temperature capacitors that employ aluminum oxynitride as the dielectric material of choice. These capacitors can also be used at high temperatures to 400 C. This, too, remains a small and custom type market.
High-Temperature Metallization & Mounting Materials
Ceramic and tantalum capacitors are available with a variety of termination/metallization materials. High-temperature designs incorporate metals such as tin, palladium-silver and gold plating which have melting points well above the temperature rating of the capacitor. These materials perform well at elevated temperatures and should be considered a critical part of the construction in such a demanding environment.
Mechanical and Thermal Performance Considerations
Mechanical Shock and Vibration – Not only is temperature an issue in the application listed previously, but mechanical performance is a major consideration in mission critical designs as well. Down-hole oil exploration, aerospace and defense electronics are among the most mechanically demanding applications in the world. Mechanical shock and vibration have a major impact on device selection and designs. In some cases, these electronic systems can experience forces in which standard technologies would catastrophically fail.
Specialty Packaging – Because of this risk of failure, custom mounting designs and plastic molded encapsulation techniques have been developed for applications requiring an advanced reliability and odd form factor.
Thermal Cycling and Thermal Shock Performance – In addition to mechanical shock and vibration, the thermal cycling effects of operation and assembly take a toll on the capacitors. During assembly, the parts may be improperly handled and even encounter thermal cracking due to hand soldering or improper heating. During operation, the capacitors can encounter temperature changes that cause significant thermal expansion/contraction of the materials and assemblies. In order to improve upon these designs and ensure that the components can withstand these effects, advanced materials have been incorporated into the termination materials.
Advancements In Polymeric Terminations and High Temperature Capacitors – Polymeric material has been incorporated into termination designs in order to absorb the effects of thermal cycling, creating a flexible termination that prevents failure.
Market Outlook
We forecast that demand for high-temperature capacitors for power supply and sensor applications will grow in value over the next five years. The continued commercialization of space, coupled with a revival in the oil and gas sector and a revival in commercial aviation, is expected to drive demand for high-temperature capacitors for use in power supplies and related high-temperature circuitry. [4]
References and Notes
[1] Dennis M. Zogbi. High Temperature Capacitors: World Markets, Technologies & Opportunities: 2016-2021. ISBN # 1-893211-90-8 (2016). Cary, North Carolina USA: Paumanok Publications, Inc.; 2021. www.paumanokgroup.com
[2] Zogbi. High Temperature Capacitors: World Markets, Technologies & Opportunities: 2016-2021.
[3] Teflon is a registered trademark of Chemours, Inc., a spin-off of DuPont. and Kapton is a Trademark of Du Pont de Nemours and Company. Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene. The commonly known brand name of PTFE-based compositions is Teflon.
[4] Zogbi. High Temperature Capacitors: World Markets, Technologies & Opportunities: 2016-2021.
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