Integrated passive devices
Integrated Passive Devices "or Integrated Passive Components or Embedded Passive Components" are electronic components where resistors, capacitors, inductors/coils/chokes, microstriplines, impedance matching elements, baluns or any combinations of them are integrated in the same package or on the same substrate. Sometimes integrated passives can also be called as embedded passives, and still the difference between integrated and embedded passives is technically unclear,. In both cases passives are realised in between dielectric layers or on the same substrate.
Earliest form of IPDs are resistor, capacitor, resistor-capacitor or resistor-capacitoR-coil networks. Passive transformers can also be realised as integrated passive devices like by putting two coils on top of each other separated by a thin dielectric layer. Sometimes diodes can be integrated on the same substrate with integrated passives specifically if the substrate is silicon or some other semiconductor like gallium arsenide.
Integrated passive devices can be packaged, bare dies/chips or even stacked in a third dimension with active integrated circuits or other IPDs in an electronic system assembly.Typical packages for integrated passives are SIL, SIP or any other packages used in electronic packaging. Integrated passives can also act as a module substrate, and therefore be part of a hybrid module.
The substrate for IPDs can be rigid like ceramic, layered ceramic , glass, and silicon, coated with some dielectric layer like silicon dioxide. The substrate can be also flexible like laminate e. g. a package interposer, FR4 or similar, Kapton or any other suitable polyimide. It is beneficial for the electronics system design if the effect of the substrate and the possible package to the performance of IPDs can be neglected or known.
Manufacturing of IPDs used include thick and thin film technologies and variety of integrated circuit processing steps or modifications of them. Integrated passives are available as standard components/parts or as custom designed devices.
Integrated passive devices are mainly used as standard parts or custom designed due to
- needs to reduce number of parts to be assembled in an electronic system resulting minimized logistics needed.
- needs to miniaturize electronics like for medical, wearable and portable use. Striplines, baluns etc can be miniaturized with IPDs with smaller tolerances in radio frequency parts of the system specifically if thin film technology is used.
- needs to reduce weight of electronic assemblies for example in space or in unmanned aerial vehicles applications
- electronic designs, which requires numerous passives with the same value like several one nanofarad capacitors. This may happen in implementations where integrated circuits with a high input/output count are needed/used. Many high speed signals or power supply lines may need stabilization by capacitors. Emergence of digital implementations leads to use digital parallel lines and stabilization of all signal lines resulting capacitor islands in the implementation. Miniaturization of those may result to use integrated capacitor networks.
- electronic designs which require numerous electromagnetic interference or electrostatic discharge suppression functionality like designs with high input/output pin count connectors in interfaces. EMI or ESD suppression typically is realized with RC or R-diode networks.
- limitations of performance and values of passive elements available in integrated circuit technologies like CMOS as monolithically integrated with active elements. If size and/or weight of electronics assembly need to be minimized and standard parts are not available, custom IPDs might be the only option towards smallest number of parts, small size or weight of electronics.
- improved reliability if interfaces between different technologies needs to be minimised
IPDs on a silicon substrate
IPDs on a silicon substrate are generally fabricated using standard wafer fabrication technologies such as thin film and photolithography processing. IPDs can be designed as flip chip mountable or wire bondable components. However to differentiate technically from IC technologies IPD technologies may utilise thicker metal or different resistive layers, thinner or different higher K dielectric layers for higher capacitance density than with typical IC technologies.IPDs on silicon can be grinded - if needed - below 100µm in thickness and with many packaging options and delivery mode options.
3D passive integration in silicon is one of the technologies used to manufacture Integrated Passive Devices, enabling high-density trench capacitors, MIM capacitors, resistors, high-Q inductors, PIN diodes or Zener diodes to be implemented in silicon. The design time of IPDs on silicon depends on complexity of the design but can be made by using same design tools and environment what is used for application specific integrated circuits. Some IPD suppliers offer full design kit support so that System in Package module manufacturers or system houses are able to design their own IPD fulfilling their specific application requirements.
History and IPDs role in electronic system assembly
In early control system design it was discovered that having same value of components makes design easier and faster. One way to implement passive components with same value or in practice with smallest possible distribution is to place them on the same substrate near to each other.Earliest form of integrated passive devices were resistor networks in the 1960's when four to eight resistors were packaged in form of Single-in-line package by Vishay Intertechnology. Many other type of packages like DILs, DIPs etc. used in packaging integrated circuits even customised packages are used for integrated passive devices. Resistor, capacitor, and resistor capacitor networks are still widely used in systems even though monolithic integration has progressed.
Today portable electronic systems include roughly 2-40 discrete passive devices/integrated circuit or module. This shows that monolithic or module integration is not capable to include all functionality based on passive components in system realisations, and variety of technologies is needed to minimize logistics and system size. This is the application area for IPDs. Most - by number - of the passives in electronic systems are typically capacitors followed by number of resistors and inductors/coils.
Many functional blocks such as impedance matching circuits, harmonic filters, couplers and baluns and power combiner/divider can be realized by IPDs technology. IPDs are generally fabricated using thin, thick film and wafer fabrication technologies such as photolithography processing. IPDs can be designed as flip chip mountable or wire bondable components.
Trends towards applications with small size, portability and wireless connectivity have stretched various implementation technologies to be able to realize passive components. Currently there are 25 - 30 companies delivering integrated passive devices worldwide.
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