In addition, personal medical-monitoring devices promise tremendous benefits for healthcare professionals and patients by helping to manage a wide variety of conditions such as diabetes, heart disease, or arrhythmia. With these personal monitors, professionals are able to improve standards of care, even with increasing numbers of patients. Patients, for their part, can enjoy more functional lives at home without having to make regular visits to a consultant.

Monitors and imaging systems often depend on precision analog signal-processing circuitry at the front end of the signal chain to condition signals such as the output of an MRI sensor, ultrasound sensor array, or the photodetector in a pulse oximeter. Other types of medical monitors, such as implantable pacemakers and cardioverter defibrillators, are life-critical and require consistently accurate performance as well as extreme reliability from all electronic components in the circuit. These include capacitors, which often have a vital role in signal conditioning, filtering, and power supply stabilization.

Medical Equipment Needs

Demands from medical equipment designers typically go well beyond those experienced in general-purpose commercial applications. Designers often need high-capacitance values in small case sizes, particularly for implantable devices. In addition, the capacitors must display very high reliability with failure rates in the low parts per million or better—over lifetimes of ten years or more. In some applications, such as implantables, the operating temperature can be assumed to be reasonably constant.

Still, the capacitance change with voltage must be minimized to maintain consistent signal-handling accuracy. On top of that, long battery life is often vital, particularly for implantables. Capacitor technologies that reduce leakage current allow applications to run longer on tiny batteries.

Delivering devices that offer the required performance and reliability means incorporating a combination of new materials and construction technologies, as well as enhanced testing and screening procedures dedicated to the needs of the medical electronics industry.

The Drive for Miniaturization

General industry-wide demand for smaller printed-circuit-board (PCB) sizes, as well as reduced cost, has pushed ceramic capacitors toward base-metal electrode (BME) technology in recent years. Typically, these use nickel in the electrode system. A nickel-based BME ensures higher voltage-stress capability compared to earlier precious-metal electrode (PME) systems, such as palladium-silver alloy.

Thanks to the higher voltage-stress capability, multi-layer ceramic capacitors (MLCCs) can be designed with thinner dielectric layers, thus increasing volumetric efficiency (capacitance per volume, or CV). Improved coating and handling processes enable manufacturers to achieve tight control when producing dielectric layers at thicknesses of than 1 µm, and today’s BME system can support hundreds of layers in the same device.