To provide a thin film capacitor in which a pair of terminal electrodes can be disposed on the same plane. A thin film capacitor includes a metal foil having a roughened upper surface, a dielectric film covering the upper surface of the metal foil and having an opening for partly exposing the metal foil therethrough, a first electrode layer contacting the metal foil through the opening, and a second electrode layer contacting the dielectric film without contacting the metal foil. With this configuration, both the first and second electrode layers can be disposed on the upper surface of the metal foil. In addition, since the metal foil is surface-roughened, a larger capacitance can be obtained.

To provide a thin film capacitor having high flexibility. A thin film capacitor includes: a metal foil having a roughened upper surface; a dielectric film covering the upper surface of the metal foil and having an opening through which the metal foil is partly exposed; a first electrode layer contacting the metal foil through the opening; and a second electrode layer contacting the dielectric film without contacting the metal foil. The particle diameter of crystal at a non-roughened center part of the metal foil is less than 15 μm in the planar direction and less than 5 μm in the thickness direction. This can not only enhance the flexibility of the metal foil to reduce a short-circuit failure in a state where the thin film capacitor is incorporated in a multilayer substrate but also enhance positional accuracy.

This application describes methods and apparatus for the safety and protection of capacitor units suitable for medium and high voltage applications, for instance within switching modules (400) of a voltage source converter as may be used for HVDC or FACTs. The capacitor unit (300) has a housing (201) within which is a capacitor comprising a plastic film dielectric material, for instance a winding (100) of first and second plastic films (101, 102) with metal coatings (103, 104). A pressure sensor (302) is configured to detect if the pressure in the housing exceeds a first pressure level and a pressure relief valve (304) is configured to vent gas from the housing if the pressure in the housing exceeds a second pressure level which is higher than the first pressure level.

This application describes methods and apparatus for the safety and protection of capacitor units suitable for medium and high voltage applications, for instance within switching modules (400) of a voltage source converter as may be used for HVDC or FACTs. The capacitor unit (300) has a housing (201) within which is a capacitor comprising a plastic film dielectric material, for instance a winding (100) of first and second plastic films (101, 102) with metal coatings (103, 104). A pressure sensor (302) is configured to detect if the pressure in the housing exceeds a first pressure level and a pressure relief valve (304) is configured to vent gas from the housing if the pressure in the housing exceeds a second pressure level which is higher than the first pressure level.

A stacked film capacitor device has less capacitance loss. The film capacitor device includes a film stack with metal layers including adjacent metal layers in 180° opposite orientations in a direction in which the metal layers extend continuously, and a first metal electrode and a second metal electrode on a pair of end faces of the film stack. At least one of a pair of end faces of the film stack in y-direction includes a recess continuously extending in a stacking direction and separating the film stack from the first metal electrode. The recess electrically insulates the metal layers serving as internal electrodes from a metal-sprayed electrode serving as an external electrode.

A film capacitor that includes a resin layer having a linear protrusion on a first surface thereof and a linear recess on a second surface thereof opposite the first surface, and a metal layer on the first surface of the resin layer. A total length of the linear recess per 1 cm.sup.2 is 3 m or less, and an average depth of the linear recess is 0.01 μm to 1.3 μm.

A film capacitor that includes a dielectric resin film having a first surface and a second surface facing each other in a thickness direction of the dielectric resin film, wherein the first surface of the dielectric resin film includes 25 to 125 of first recesses each having a long diameter of 30 nm to 800 nm per an area of 5 μm×5 μm; and a metal layer on the first surface of the dielectric resin film.

A capacitor includes: a capacitor element; a pair of external electrodes provided at opposite ends of the capacitor element; and a pair of metal caps and or a metal foil, the pair of metal caps each covering a corresponding one of the pair of external electrodes, the metal foil covering at least part of the capacitor element.

A capacitor cell element includes a dielectric, which has a first metal coating on a first side and has a second metal coating on a second side. The first metal coating on the first side leaves free a first edge region, and the second metal coating on the second side leaves free a second edge region. The first edge region and the second edge region are disposed at opposite ends of the dielectric. A capacitor including the capacitor cell element is also provided. The capacitor cell element and the capacitor have a high volumetric energy density and at the same time are self-healing.

A capacitor cell element includes a dielectric, which has a first metal coating on a first side and has a second metal coating on a second side. The first metal coating on the first side leaves free a first edge region, and the second metal coating on the second side leaves free a second edge region. The first edge region and the second edge region are disposed at opposite ends of the dielectric. A capacitor including the capacitor cell element is also provided. The capacitor cell element and the capacitor have a high volumetric energy density and at the same time are self-healing.