85.41 Semiconductor devices (for example, diodes, transistors, semiconductor-based transducers); photosensitive semiconductor devices, including photovoltaic cells whether or not assembled in modules or made up into panels; light-emitting diodes (LED), whether or not assembled with other light-emitting diodes (LED); mounted piezo-electric crystals..

(A) SEMICONDUCTOR DEVICES (FOR EXAMPLE DIODES, TRANSISTORS, SEMICONDUCTOR BASED TRANSDUCERS)
These are defined in Note 12 (a) (ⅰ) to this Chapter.
The operation of the devices of this group is based on the electronic properties of certain "semiconductor" materials or, for the purpose of semiconductor-based transducers, on their semiconductor properties including physical (e.g., mechanical, thermal), electrical, optical and chemical properties.
The main characteristics of these materials is that at room temperature their resistivity lies in the range between that of conductors (metals) and that of insulators. They consist, for instance, of certain ores (e.g., crystal galena), tetravalent chemical elements (germanium, silicon, etc.) or combinations of chemical elements (e.g., trivalent and pentavalent elements, such as gallium arsenide, indium antimonide).
Semiconductor materials consisting of a tetravalent chemical element are generally monocrystalline. They are not used in their pure state but after very light doping (in a proportion expressed in parts per million) with a specific "impurity" (dopant).
For a tetravalent element, the "impurity" may be a pentavalent chemical element (phosphorus, arsenic, antimony, etc.) or a trivalent element (boron, aluminium, gallium, indium, etc.). The former produce n-type semiconductors with excess electrons (negatively charged); the latter produce p-type semiconductors with electron deficiency, that is to say that holes (positively charged) predominate.
Semiconductor materials combining tri- and pentavalent chemical elements are also doped.
In the semiconductor materials consisting of ores, the impurities contained naturally in the ore act as dopants.
The semiconductor devices of this group generally comprise one or more "junctions", between p-type and n-type semiconductor materials.
They include :

(Ⅰ) Diodes which are two terminal devices with a single p n junction; they allow current to pass in one direction (forward) but offer a very high resistance in the other (reverse). They are used for detection, rectification, switching, etc.
The main types of diodes are signal diodes, power rectifier diodes, voltage regulator diodes, voltage reference diodes.

(Ⅱ) Transistors are three- or four-terminal devices capable of amplification, oscillation, frequency conversion, or switching of electrical currents. The operation of a transistor depends on the variation in resistivity between two of the terminals upon the application of an electric field to the third terminal. The applied control signal or field is weaker than the resulting action brought about by the change in resistance and thus amplification results.
Transistors include :

(1) Bipolar transistors, which are three terminal devices consisting of two diode type junctions, and whose transistor action depends on both positive and negative charge carriers (hence, bipolar).

(2) Field effect transistors (also known as metal oxide semiconductors (MOS)), which may or may not have a junction, but which depend on the induced depletion (or enhancement) of available charge carriers between two of the terminals. The transistor action in a field effect transistor employs only one type of charge carrier (hence, unipolar). A parasitic body diode, which is produced in a MOS type transistor (also known as MOSFET), may operate as a freewheeling diode during inductive load switching. MOSFET which have four terminals are known as tetrodes.

(3) Insulated Gate Bipolar Transistors (IGBT), which are three-terminal devices consisting of a gate terminal and two load terminals (emitter and collector). By applying appropriate voltages across the gate and emitter terminals, current in one direction can be controlled, i.e. turned on and turned off. IGBT chips may be incorporated with diodes in a single package (packaged IGBT devices), which protect the IGBT device and allow it to continue to function as a transistor.

(Ⅲ) Semiconductor-based transducers
As specified in Note 12 (a) (ⅰ) to this Chapter, these are devices in which the semiconductor substrate or material plays a critical and irreplaceable role in performing their function to convert any kind of physical or chemical phenomena or an action into an electrical signal or an electrical signal into any type of physical phenomenon or an action.
As specified in Note 12 (a) (ⅰ) to this Chapter, these are devices in which the semiconductor substrate or material plays a critical and irreplaceable role in performing their function to convert any kind of physical or chemical phenomena or an action into an electrical signal or an electrical signal into any type of physical phenomenon or an action.
The semiconductor-based transducers have the character of an independent technical unit, and can be presented either as bare die products or in a package. The components forming a semiconductor-based transducer, including active or passive discrete components indivisibly attached that enable their construction or function, must be combined to all intents and purposes indivisibly, i.e., though some of the components could theoretically be removed and replaced, this would be uneconomic under normal manufacturing conditions. Non-semiconductor-based components which do not play a key role in transducers are allowed to be part of the transducer in situations when they contribute to the transducer’s function as a sensor, actuator, resonator or oscillator. Typical examples of such components are, but not limited to, the following:

(ⅰ) the package, which typically consists of metal wires for interconnection (internal or external wirebond connections), a leadframe, an encapsulation, substrates etc.; or

(ⅱ) components which enable or support the function like magnets, optical elements etc.

The definition of the expression "semiconductor-based" also includes elements in which the semiconductor material provides functionality to the transducer by its properties, which are not only semiconductor-specific. Such properties may include mechanical strength, flexibility, thermal conductivity, optical reflectivity, chemical resistivity, etc., in combination with its ability to be manufactured with high precision on a micrometer scale by using semiconductor technology (micro machining). Such elements may include, for example membranes, bars, cantilevers, cavities, mirrors, channels, etc., which enable transducer functions by thickness or elastic flexibility).
The materials used in semiconductor-based transducers include e.g., Silicon (Si), Germanium (Ge), Carbon (C), Silicon Germanium (SiGe), Silicon Carbide (SiC), Gallium Nitride (GaN), Gallium Arsenide (GaAs), Indium Gallium Arsenide InGaAs, Gallium Phosphide (GaP), Indium Phosphide (InP), Tin Telluride (SnTe), Zinc Oxide (ZnO) and Gallium Oxide (Ga2O3).
The expression "manufactured by semiconductor technology" means the application of area processing on a wafer level that may include grinding, polishing, doping, spin coating, imaging, CVD, PVD, galvanic, developing, stripping, etching, baking, printing.
The types of semiconductor-based transducers are:

(1) Semiconductor-based sensors, which are defined in Note 12 (a) (ⅰ) (3).
One example of a sensor is a Micro-Electro-Mechanical Systems (MEMS) element used in silicon microphones as a semiconductor-based acoustic sensor. The MEMS element is made up of a stiff and perforated backplate and a flexible membrane on silicon substrate, and its function is to convert sound waves into a variable electrical output. Sound waves are physical quantities that hit the membrane and bring it to vibration through which the varying electrical output is produced.
Another type of sensor is a gas sensor, which utilises the adsorption of electron donors/acceptors to change the resistance in graphene with an extremely high surface area.

(2) Semiconductor-based actuators, which are defined in Note 12 (a) (ⅰ) (4), e.g., electro-thermally actuated Micro-Electro-Mechanical Systems (MEMS) mirrors, which are typically used to deflect a laser beam in a broad range of applications, such as fibre-to-fibre optical switching, laser projectors, Light Detection and Ranging (LIDAR) in autonomous driving, laser tracking and position measurement, etc. Electro-thermally actuated mirrors are moved by heater elements, which act on semiconductor-based structures with different thermal expansion.

(3) Semiconductor-based resonators, which are defined in Note 12 (a) (ⅰ) (5), e.g., film bar acoustic wave resonators (FBAR), which are used in RF technology for multiplexing or channel selection in wireless devices.

(4) Semiconductor-based oscillators, which are defined in Note 12 (a) (ⅰ) (6), converting physical phenomena (stored energy of electromagnetic fields inside a resonator) into an electrical signal (output voltage with frequency depending on tuning voltage).

(Ⅳ) Other semiconductor devices
They include :

(1) Thyristors, consisting of four conductivity regions in semiconducting materials (three or more p n junctions) through which a direct current passes in a predetermined direction when a control pulse initiates conductivity. They are used as controlled rectifiers, as switches or as amplifiers and function as two interlocking, complementary transistors with a common collector/base junction.

(2) Triacs (bi directional triode thyristors), consisting of five conductivity regions in semiconducting materials (four p n junctions) through which an alternating current passes when a control pulse initiates conductivity.

(3) Diacs, consisting of three conductivity regions in semiconducting materials (two p n junctions) and used to provide the pulses required to operate a triac.

(4) Varactors (or variable capacitance diodes).

(5) Field effect devices, such as gridistors.

(6) Gunn effect devices.
However, this group does not include semiconductor devices which differ from those described above in that their operation depends primarily on temperature, pressure, etc., such as non linear semiconductor resistors (thermistors, varistors, magneto resistors, etc.) (heading 85.33).
For photosensitive devices the operation of which depends on light rays (photodiodes, etc.), see group (B).
The devices described above fall in this heading whether presented mounted, that is to say, with their terminals or leads (for example pins, leads, balls, lands, bumps or pads mounted on a carrier, e.g., a substrate or a leadframe) or packaged (components), unmounted (elements) or even in the form of undiced discs (wafers). However, natural semiconductor materials (e.g., galena) are classified in this heading only when mounted.
The semiconductor-based transducers of this group, however, do not cover silicon based sensors, actuators, resonators, oscillators and combinations thereof, containing one or more monolithic, hybrid, multi-chip or multi-component integrated circuits as defined in Note 12 (b) (ⅳ) (3) to this Chapter (heading 85.42).
The heading also excludes:

(a) Chemical elements (for example, silicon and selenium) doped for use in electronics, in forms unworked as drawn, or in the form of cylinders or rods (Chapter 28), when cut in the form of discs, wafers or similar forms (heading 38.18).

(b) Chemical compounds such as cadmium selenide and sulphide, indium arsenide, etc., containing certain additives (e.g., germanium, iodine) generally in a proportion of a few per cent, with a view to their use in electronics, whether in the form of cylinders, rods, etc., or cut into discs, wafers or similar forms (heading 38.18).

(c) Crystals doped for use in electronics, in the form of discs, wafers, or similar forms, polished or not, whether or not coated with a uniform epitaxial layer, provided they have not been selectively doped or diffused to create discrete regions (heading 38.18).

(d) Electronic integrated circuits (heading 85.42).

(e) Micro-assemblies of the moulded module, micromodule or similar types, consisting of discrete, active or both active and passive, components which are combined and interconnected (generally Chapters 84, 85 or 90).

(B) PHOTOSENSITIVE SEMICONDUCTOR DEVICES
This group comprises photosensitive semiconductor devices in which the action of visible rays, infra red rays or ultra violet rays causes variations in resistivity or generates an electromotive force, by the internal photoelectric effect.
Photoemissive tubes (photoemissive cells) the operation of which is based on the external photoelectric effect (photoemission), belong to heading 85.40.
The main types of photosensitive semiconductor devices are :

(1) Photoconductive cells (light dependent resistors), usually consisting of two electrodes between which is a semiconductor substance (cadmium sulphide, lead sulphide, etc.) whose electrical resistance varies with the intensity of illumination falling on the cell.
These cells are used in flame detectors, in exposure meters for automatic cameras, for counting moving objects, for automatic precision measuring devices, in automatic door opening systems, etc.

(2) Photovoltaic cells, which convert light directly into electrical energy without the need for an external source of current. Photovoltaic cells based on selenium are used mainly in luxmeters and exposure meters. Those based on silicon have a higher output and are used, in particular, in control and regulating equipment, for detecting light impulses, in communication systems using fibre optics, etc.
Special categories of photovoltaic cells are :

(ⅰ) Solar cells, silicon photovoltaic cells which convert sunlight directly into electric energy. They are usually used in groups as sources of electric power, e.g., in rockets or satellites employed in space research, for mountain rescue transmitters.
The heading also covers solar cells, whether or not assembled in modules or made up into panels. However the heading does not cover panels or modules equipped with elements, however simple, (for example, diodes to control the direction of the current), which supply the power directly to, for example, a motor, an electrolyser (heading 85.01).

(ⅱ) Photodiodes (germanium, silicon, etc.), characterised by a variation in resistivity when light rays strike their p n junction. They are used in automatic data processing (reading of data storage), as photocathodes in certain electronic tubes, in radiation pyrometers, etc. Phototransistors and photothyristors belong to this category of photoelectric receivers.
The devices of this category differ, when packaged, from the diodes, transistors and thyristors of Part (A) above by their housing, which is partly transparent to permit the passage of light.

(ⅲ) Photocouples and photorelays consisting of electroluminescent diodes combined with photodiodes, phototransistors or photothyristors.
Photosensitive semiconductor devices fall in this heading whether presented mounted (i.e., with their terminals or leads), packaged or unmounted.

(C) LIGHT-EMITTING DIODES (LED)
Light-emitting diodes (LED), or electroluminescent diodes (based, inter alia, on gallium arsenide, gallium phosphide or gallium nitride) are devices which convert electric energy into visible, infra-red or ultra-violet rays. They are used, e.g., for displaying or transmitting data in control systems or for illumination and lighting applications.
Laser diodes emit a coherent light beam and are used, e.g., in detecting nuclear particles, in altimetering or in telemetering equipment, in communication systems using fibre optics.
This group also includes :

(1) Light-emitting diode (LED) packages
These are single electrical components encapsulating principally one or more light-emitting diode (LED) chips (dies), and possibly including optical elements and thermal, mechanical, and electrical interfaces (e.g. electric connectors including wires to connect with external control circuitry).
Protective diodes (e.g. Zener diodes) may be connected anti-parallel to the Gallium-nitride-based light-emitting Diode (GaN LED) chips to protect the GaN LED chips from electrostatic discharge for some of GaN LED packages.
There are two basic types of white LED packages. The first type is composed of a combination of LED chip(s) and fluorescent material (phosphor).
The second type of white LED packages is composed of a combination of red LED chip(s), green LED chip(s) and blue LED chip(s). White LED packages are used for general lighting and backlight applications.

(2) Light-emitting diode (LED) assemblies
These are assemblies comprised of light-emitting diode (LED) packages mounted on a printed circuit board, which may include optical elements and thermal, mechanical, and electrical interfaces (e.g., electric connectors including wires to connect with external control circuitry).
The LED assemblies do not have the control circuitry necessary to rectify AC power and control DC current to a level usable by the LEDs.
The number of LEDs does not alter the function of the LEDs but contributes only to the intensity of the light.
Certain LED assemblies use LED chips instead of LED packages. The chips are mounted on a printed circuit board and encapsulated overall or individually, possibly with phosphor.

(D) MOUNTED PIEZO ELECTRIC CRYSTALS
These are mainly barium titanate (including polycrystalline polarised elements of barium titanate), lead titanate zirconate or other crystals of heading 38.24 (see the corresponding Explanatory Note), or quartz or tourmaline crystals. They are used in microphones, loudspeakers, ultrasonic apparatus, stabilised frequency oscillating circuits, etc. They are classified here only if mounted. They are generally in the form of plates, bars, discs, rings, etc., and must, at least, be equipped with electrodes or electric connections. They may be coated with graphite, varnish, etc., or arranged on supports and they are often inside an envelope (e.g., metal box, glass bulb). If, however, because of the addition of other components, the complete article (mounting plus crystal) can no longer be regarded as merely a mounted crystal but has become identifiable as a specific part of a machine or appliance, the assembly is classified as a part of the machine or appliance in question : e.g., piezo electric cells for microphones or loudspeakers (heading 85.18), sound-heads (heading 85.22), pick up elements (feelers) for ultrasonic thickness measuring or detecting instruments (generally classified in accordance with Note 2 (b) to Chapter 90 or in heading 90.33, as the case may be), quartz oscillators for electronic watches (heading 91.14).
This heading also excludes unmounted piezo electric crystals (generally heading 38.24, 71.03 or 71.04).

Subheading Explanatory Note.

Subheading 8541.21
The dissipation rate of a transistor is measured by applying the specified operating voltage to the device and measuring the continuous power handling capability using a case temperature limit of 25º C. For example, if a transistor is capable of handling a 0.2 ampere load continuously at a specified operating voltage of five volts while maintaining a case temperature of 25º C, its dissipation rate is 1 watt (Amperage x Voltage = Wattage).
For transistors with a means of heat dissipation (for example, a tab, a metal case), the reference temperature of 25º C is that of the bottom or of the case, whereas for other transistors (for example, with simple casing of plastics), the room temperature applies.

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