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Researchers Submit Patent Application, "Optoelectronic Semiconductor Chip, Display Comprising a Semiconductor Chip of This Type, and Use of a...

August 20, 2014



Researchers Submit Patent Application, "Optoelectronic Semiconductor Chip, Display Comprising a Semiconductor Chip of This Type, and Use of a Semiconductor Chip of This Type Or of a Display", for Approval

By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Behringer, Martin Rudolf (Regensburg, DE); Guenther, Oliver (Rueckersdorf, DE), filed on June 6, 2012, was made available online on August 7, 2014.

The patent's assignee is Osram Opto Semiconductors Gmbh.

News editors obtained the following quote from the background information supplied by the inventors: "Semiconductor chips such as, for example, light-emitting diodes (LEDs) age more rapidly under the influence of moisture than in a dry atmosphere. This ageing process is based, inter alia, on corrosion effects and leakage currents in or at the semiconductor chip. This ageing process is particularly pronounced when the LEDs are not operated, since the latter are then at a lower temperature than in the operating state, as a result of which a film of liquid can form, for example, directly on the semiconductor chip on account of condensation of moisture stored in the air. A liquid film of this type disadvantageously fosters and accelerates the degradation of the semiconductor chip.

"Furthermore, the wavelength of the radiation emitted by the semiconductor chip disadvantageously shifts with a change of temperature in the semiconductor chip. By way of example, such a wavelength shift based on temperature changes can occur upon switch-on and start-up of the semiconductor chip or during pulsed operation of the semiconductor chip.

"In order to reduce the above mentioned disadvantages of the ageing effects and wavelength shifts, it is conventionally known, for example, to form a protective housing or a protective coating on the semiconductor chip, which keep the moisture away from the semiconductor chip and thus make the semiconductor chip more stable against corrosion at the expense of the luminous efficiency and radiation efficiency."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Embodiments of the present application specify a semiconductor chip which avoids the disadvantages mentioned above, thereby advantageously resulting in an ageing-stable semiconductor chip which has an optimum luminous efficiency and, in addition, a small wavelength shift on account of reduced temperature changes in the semiconductor chip.

"In one embodiment, the optoelectronic semiconductor chip comprises a semiconductor layer sequence having an active layer provided for generating radiation. The semiconductor chip can be operated in a first operating mode and in a second operating mode. The semiconductor layer sequence emits radiation in the first operating mode. The semiconductor layer sequence emits no radiation in the second operating mode. The semiconductor layer sequence is operated in the forward direction in the first operating mode and in the reverse direction in the second operating mode. In other words, the semiconductor chip can be operated in two separate operating modes that are different from one another.

"The semiconductor chip thus has two operating modes, wherein the semiconductor chip emits radiation only in the first operating mode. Accordingly, the second operating mode should be regarded as an optically switched-off operating state with regard to the emission of radiation. According to the invention, in this case the semiconductor chip is operated with a current in the reverse direction in said optically switched-off operating state. Operation in the reverse direction and not in the forward direction serves, in particular, the purpose that the semiconductor chip emits no radiation in the second operating mode.

"As a result of operation in the reverse direction, the semiconductor chip is advantageously heated without emitting radiation in the process, as a result of which condensation effects at the semiconductor chip which can occur on account of moisture occurring in the environment of the semiconductor chip are advantageously reduced. As a result, it is advantageously possible to obtain a longer lifetime of semiconductor chips of this type in moist environments. A moist environment is considered to be, in particular, an environment in which condensation effects can occur when the semiconductor chip is not operated, such as, for example, in the tropics, by the sea or at night.

"Alongside the moisture stability, a semiconductor chip of this type is additionally distinguished by a wavelength stability of the radiation emitted by the semiconductor chip during pulsed operation, since the semiconductor chip can be kept at a higher temperature even in the optically switched-off operating state on account of the energization in the reverse direction. Furthermore, the warm-up time of semiconductor chips of this type can thus be shortened, as a result of which they can attain their predetermined operating performance (so-called 'steady state') significantly more rapidly. This is advantageous particularly in the case of displays comprising a plurality of semiconductor chips.

"In connection with the present application, 'operation' means that the semiconductor chip can be acted on externally in a predeterminable manner with electric current, impression of electrostatic charge into the semiconductor chip or into individual components of the semiconductor chip and/or application of electrical voltage to the semiconductor chip, such that the active layer of the semiconductor chip is suitable for emitting electromagnetic radiation.

"'Operation of the semiconductor chip in two operating modes' means that that semiconductor chip can be set externally in a predeterminable manner in each operating mode, for example, with regard to the operating parameters, the energization level, operating current, operating voltage, operating duration, operating temperature and/or impression level of electrical charges into the semiconductor chip.

"Operating the semiconductor layer sequence in the reverse direction means that a reverse current flows through the semiconductor layer sequence. In this case, the reverse direction is in the opposite direction to the forward direction.

"The semiconductor chip is an optoelectronic semiconductor chip which makes it possible to convert electrically generated data or energies into light emission, or vice versa. By way of example, the optoelectronic semiconductor chip is a radiation-emitting semiconductor chip, for example an LED.

"The active layer of the semiconductor layer sequence preferably contains a pn-junction, a double hetero structure, a single quantum well (SQW) structure or a multi quantum well (MQW) structure for generating radiation. In this case, the designation quantum well structure does not manifest any significance with regard to the dimensionality of the quantization. It encompasses, inter alia, quantum wells, quantum wires and quantum dots and any combination of these structures.

"The semiconductor chip, in particular the active layer, preferably contains a III/V semiconductor material. III/V semiconductor materials are particularly suitable for generating radiation in the ultraviolet, through the visible right into the infrared spectral range. The semiconductor chip comprises a plurality of semiconductor layers which are deposited epitaxially one on top of another and in which the active layer is arranged. By way of example, the layers of the semiconductor chip are grown on a growth substrate. In this case, the active layer separates a p-doped side of the semiconductor chip from an n-doped side of the semiconductor chip.

"In accordance with at least one embodiment, the semiconductor chip comprises at least one drive device for operating the semiconductor chip in the first operating mode and in the second operating mode. Accordingly, the drive device operates the semiconductor chip in the first operating mode or in the second operating mode in a predeterminable manner. Accordingly, the drive circuit acts on the semiconductor chip with electric current in a predeterminable manner. In this case, the drive device acts on the semiconductor chip with current in the reverse direction in the second operating mode and with current in the forward direction in the first operating mode. Accordingly, the semiconductor chip can be operated in both operating modes with a single drive device.

"In accordance with at least one embodiment, a leakage path is formed in the semiconductor layer sequence, a predetermined reverse current flowing via said leakage path in the second operating mode. This means that not all of the semiconductor layer sequence is operated in the reverse direction. A leakage path is incorporated in the semiconductor layer sequence, the defined and predetermined reverse current flowing via said leakage path upon reverse-biasing in the second operating mode. The semiconductor chip can thus advantageously be heated in the second operating mode.

"In accordance with at least one embodiment, a passivation layer is arranged on the semiconductor layer sequence, wherein the leakage path is implemented via the passivation layer. Preferably, the leakage path via the semiconductor layer sequence or a contact structure of the semiconductor chip is created such that, upon forward-biasing of the semiconductor chip, that is to say in the first operating mode, no or only a negligible current flows and, upon reverse-biasing, that is to say in the second operating mode, at a small voltage sufficient current flows to ensure the desired increase in temperature of the semiconductor layer sequence.

"In accordance with at least one embodiment, a first operating current flows in the forward direction through the semiconductor layer sequence in the first operating mode, and a second operating current flows in the reverse direction in the second operating mode. In this case, an absolute value of a current intensity of the second operating current is preferably less than an absolute value of a current intensity of the first operating current.

"The 'absolute value' should be understood to mean, in particular, the modulus, that is to say magnitude, of the respective current intensity, which, in particular, is always a non-negative number. The absolute value corresponds, in particular, to the level of the current intensity, independently of the direction in which the operating current flows.

"In accordance with at least one embodiment, the absolute value of the current intensity of the second operating current is 10% or less of the absolute value of the current intensity of the first operating current. In this case, therefore, the absolute value of the current intensity of the second operating current is 0.1 times less than the absolute value of the current intensity of the first operating current. Accordingly, in the second operating mode, in the reverse direction only a small current flows which, in particular, is suitable for heating the semiconductor layer sequence, that is to say for increasing the temperature thereof in a predetermined manner.

"In accordance with at least one embodiment, in the second operating mode a temperature of the semiconductor layer sequence is higher by at least 2.degree. C. than a temperature of the semiconductor layer sequence in a switched-off operating state. In this case, the temperature increase in the second operating mode is based on the operation of the semiconductor layer sequence in the reverse direction.

"The switched-off operating state is, in particular, not only the optically switched-off operating state. In the switched-off operating state, in particular no current flows through the semiconductor layer sequence. 'No current flowing' should be understood to mean, in particular, that neither in the forward direction nor in the reverse direction does a current flow through the semiconductor layer sequence.

"In accordance with at least one embodiment, in the second operating mode the temperature of the semiconductor layer sequence is higher by about 10.degree. C. than the temperature of the semiconductor layer sequence in the switched-off operating state.

"In accordance with at least one embodiment, in the second operating mode a temperature of the semiconductor layer sequence is higher than an ambient temperature. 'Ambient temperature' should be understood to mean, in particular, the temperature of the environment that surrounds the semiconductor chip, that is to say, for example, the air temperature for the case where the semiconductor chip is arranged in a room. In the second operating mode, the semiconductor chip is heated in comparison with the surrounding environment, such that the condensation effect advantageously does not occur or occurs only to a reduced extent, such that the lifetime of the semiconductor chip is advantageously lengthened.

"In accordance with at least one embodiment, a display comprises a plurality of semiconductor chips which can be operated in two operating modes, wherein the semiconductor layer sequence of the semiconductor chips emits radiation in the first operating mode, emits no radiation in the second operating mode, and is operated in the forward direction in the first operating mode and in the reverse direction in the second operating mode.

"In this case, the semiconductor chips can be arranged, for example, alongside one another on a common carrier.

"In accordance with at least one embodiment, a semiconductor chip which can be operated in the first and second operating modes is used as a motor vehicle headlight. Precisely in the case of motor vehicle headlights there is the risk of condensation of moisture on the semiconductor chips of the headlight, which can disadvantageously lead to a degradation of the headlights. This risk can advantageously be counteracted with semiconductor chips operated in the reverse direction in the second operating mode.

"The features mentioned in connection with the semiconductor chip are also used in association with the display and the application as a motor vehicle headlight, and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

"Further advantages and advantageous developments of the invention will become apparent from the exemplary embodiments described below in conjunction with FIGS. 1 to 3.

"FIGS. 1A and 1B show a schematic cross section of an exemplary embodiment of a semiconductor chip according to the invention in the first and second operating mode, respectively;

"FIGS. 2A and 2B respectively show a diagram illustrating the respective operating mode and the respective operating current as a function of the operating time; and

"FIG. 3 shows a schematic cross section of an exemplary embodiment of a motor vehicle headlight according to the invention.

"In the figures, identical of identically acting component parts may in each case be provided with the same reference symbols. The component parts illustrated and their size relationships among one another should not be regarded as true to scale. Rather, individual component parts such as, for example, layers, structures, components and regions may be illustrated with exaggerated thickness or size dimensions in order to enable better illustration and/or in order to afford a better understanding."

For additional information on this patent application, see: Behringer, Martin Rudolf; Guenther, Oliver. Optoelectronic Semiconductor Chip, Display Comprising a Semiconductor Chip of This Type, and Use of a Semiconductor Chip of This Type Or of a Display. Filed June 6, 2012 and posted August 7, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5324&p=107&f=G&l=50&d=PG01&S1=20140731.PD.&OS=PD/20140731&RS=PD/20140731

Keywords for this news article include: Optoelectronics, Osram Opto Semiconductors Gmbh.

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Source: Electronics Newsweekly


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