WO1993007647A1 - A monolithic optocoupler - Google Patents

A monolithic optocoupler Download PDF

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Publication number
WO1993007647A1
WO1993007647A1 PCT/SE1992/000580 SE9200580W WO9307647A1 WO 1993007647 A1 WO1993007647 A1 WO 1993007647A1 SE 9200580 W SE9200580 W SE 9200580W WO 9307647 A1 WO9307647 A1 WO 9307647A1
Authority
WO
WIPO (PCT)
Prior art keywords
light
emitting diode
substrate
monolithic
monolithic optocoupler
Prior art date
Application number
PCT/SE1992/000580
Other languages
French (fr)
Inventor
Karl Bergman
Bo Breitholtz
Original Assignee
Asea Brown Boveri Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to SE9102844A priority Critical patent/SE469204B/en
Priority to SE9102844-9 priority
Application filed by Asea Brown Boveri Ab filed Critical Asea Brown Boveri Ab
Publication of WO1993007647A1 publication Critical patent/WO1993007647A1/en

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Classifications

    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H01L31/00Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/12Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof structurally associated with, e.g. formed in or on a common substrate with, one or more electric light sources, e.g. electroluminescent light sources, and electrically or optically coupled thereto
    • H01L31/16Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof structurally associated with, e.g. formed in or on a common substrate with, one or more electric light sources, e.g. electroluminescent light sources, and electrically or optically coupled thereto the semiconductor device sensitive to radiation being controlled by the light source or sources
    • H01L31/167Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof structurally associated with, e.g. formed in or on a common substrate with, one or more electric light sources, e.g. electroluminescent light sources, and electrically or optically coupled thereto the semiconductor device sensitive to radiation being controlled by the light source or sources the light sources and the devices sensitive to radiation all being semiconductor devices characterised by at least one potential or surface barrier
    • H01L31/173Semiconductor devices sensitive to infra-red radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus peculiar to the manufacture or treatment thereof or of parts thereof; Details thereof structurally associated with, e.g. formed in or on a common substrate with, one or more electric light sources, e.g. electroluminescent light sources, and electrically or optically coupled thereto the semiconductor device sensitive to radiation being controlled by the light source or sources the light sources and the devices sensitive to radiation all being semiconductor devices characterised by at least one potential or surface barrier formed in, or on, a common substrate

Abstract

A monolithic optocoupler consists of a light-emitting diode (2) and a photo-diode (3) mutually spaced on the surface of a semi-conductor substrate, for example an intrinsic-conduction InP substrate. According to the invention, one or more resistive channels (7) are disposed between the light-emitting diode (2) and the photo-diode (3), thereby greatly improving the breakdown properties of the structure.

Description

A Monolithic Optocoupler

Optocouplers are, today, common components which func-

5 ti.on to transmi.t si.gnals between mutually isolated • f circuits and the like. They comprise a light-emitting t diode, which can be supplied from one side, and on the other side a detector, which detects light signals arriving from the light-emitting diode. The components

10 are normally comprised of a light-emitting diode and a photo-diode, which are mounted in one and the same capsule.

A monolithic optocoupler is known from US-A 3,229,104,

15 according to which a photo-diode and a light-emitting diode are produced on one and the same semi-conductor substrate. This construction affords obvious advantages. For example, it allows a large number of optocouplers to be produced at one and the same time on one and the same

20 substrate plate, which is then divided and the compo¬ nents mounted in capsules in a known manner. However, difficulties relating to electrical insulation are experienced, such insulation being a main purpose of optocouplers, particularly when high voltages are

25 present between the circuits to be coupled. Thus, a standard requirement with regard to optocouplers is normally that an optocoupler shall be capable of with¬ standing 4 kV DC without breakthrough. This can readily be achieved with two separate, capsule-mounted co po-

30 nents, but not with monolithic optocouplers.

In the case of one known optocoupler, such as princi¬ pally illustrated in Figure 1, a light-emitting diode 2 is placed on one end of a "semi-insulating" substrate 1 35 and a photo-diode is placed on the other end of the substrate. The components are embedded in plastic and the light emitted by the light-emitting diode is transmitted through the substrate, which may, for instance, consist of indium phosphide or gallium arsenide. Indium phosphide has, for instance, a refraction index of about 3.5 for the wavelengths con-. cerned (1.0-1.67 μm) . The encapsulating material may for example be an epoxy resin which may be provided with a filler which is "white" in the wavelength range.

By "light-emitting diode" is meant here all types of light-emitting diodes, including simple light-emitting diodes and also light-emitting diodes which produce coherent radiation, so-called semi-conductor lasers with double heterostructures, and so on, these diodes being considered equivalent to one another from the aspect of the present invention.

Unfortunately, a known component of this kind has a high breakthrough tendency even when the voltage between the components is moderate. The object of the present invention is to provide a monolithic optocoupler which is less prone to breakthrough than known optocouplers.

This object is achieved in accordance with the invention by forming an electrically conductive channel on the substrate surface between the light-emitting diode and the light detector.

Although, in principle, this implies a departure from the concept of the best possible isolation, it is as¬ sumed that the inventive effect is achieved because the construction results in equalizing voltage gradients which would otherwise initiate a breakthrough process. The term "channel" shall not be understood to mean a space-limitation, but may, for instance, be understood to denote a large percentage of the substrate surface located between the components, or even the whole of this surface.

In accordance with one particular embodiment of the invention, a further improvement can be achieved by■ placing a filter layer of suitable bandgap between the light-emitting diode and the substrate, thereby enabling a large proportion of those photons from the spectrum of the light-emitting diode that have the highest energy to be eliminated. These photons would otherwise generate charge carriers in the substrate which are disposed towards causing a voltage breakthrough. It is particularly important to eliminate those photons which have the highest energy, since the cross-section of the photoelectric effect tends, in certain cases, to be highly energy dependent. A particularly good effect can be achieved by combining a gradient-equalizing resistive channel with minimization of photons which generate photoconductivity. A resistive channel according to the invention can be obtained in different ways. According to one preferred embodiment, in which the substrate is comprised of semi- insulating indium phosphide, there is employed an ion implantation technique using 100 kV helium ions in an

14 2 amount of about 10 per cm , in the form of a pair of parallel bands having a width of 10 μm. However, the main criterion is to obtain a suitably balanced high resistance across the optocoupler, for instance a resis¬ tance in the order of 100 Mohm. The resistivity is normally highly temperature-dependent, although this does not influence the inventive effect to any great extent.

The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings, in which Figure 1 illustrates a known monolithic optocoupler, as before mentioned;

Figure 2 is a principle, highly schematic perspective view of the inventive monolithic optocoupler, which has not yet been encapsulated;

Figure 3 is a sectioned view of one-half of a monolithic optocoupler constructed in accordance with one exempli- fying embodiment of the invention and shows the opto¬ coupler in more detail; and

Figure 4 is a view similar to Figure 3 and illustrates another embodiment of the invention.

The principle drawing of Figure 2 illustrates an opto¬ coupler which comprises a substrate 1 having mounted thereon a light-emitting diode 2 and a photo-diode 3. The diodes may be different but can also be identically the same, since one and the same diode can serve either as a light-emitting diode or as a photo-diode, depending on how they are connected. Although not shown, the photo-diode or detector 3 may have a different construc¬ tion, for instance may be constructed as a photo-tran- sistor, without departing from the principle of the invention. Two resistively conducting, extremely high- ohmic bands 7 have been placed between the "components" 2 and 3, thereby achieving, in accordance with the invention, a suitable, equalized voltage gradient across the "semi-insulating" (intrinsic conduction) substrate.

Figure 3 illustrates by way of example a configuration which, can be used both as a photo-diode and as a light- emitting diode and which is constructed in accordance with the following criteria: Example

A large number of monolithic optocouplers were manufac¬ tured from an In P substrate that had a thickness of 0.25 mm and doped with Fe (or Ti) to semi-insulation

+ 6 8

(intrinsic conduction n 10 -10 ohmcm) , this substrate being commercially available. Each of the optocouplers manufactured comprised two mutually spaced diode arrays 2, 3, having a first doped n -layer 20 provided with a lead-in electrode 21, an active not-intentionally doped n -layer 22, a p-layer 23, a contact layer 24 and a lead-in electrode 25 (Figure 3) . When a forward voltage is applied, such a diode array will function as a light- emitting diode, and, conversely, will function as a photo-diode when an inverse or reverse voltage is ap¬ plied. Ions were implanted in the substrate surface between these two components in two 10 μ bands 7 with

14 2

100 Kv He-ions with 10 ions per cm . The substrate was then divided into separate components, 6 mm long and 0.5 mm wide, with diode arrays at each end thereof, said diode arrays being connected by the two ion-implanted bands.

(For the purpose of improving the signal-noise ratio, or for other reasons, it is sometimes suitable to arrange more light-emitting diodes and/or more photo-diodes in one and the same component) .

The components were provided with lead-in conductors in a conventional manner and encapsulated in epoxy resin. A resistance of 100 Moh was measured between two lead-in electrodes 21. When tested, the components were found to withstand in operation a voltage of 4 kV, both DC and AC rms.

According to one preferred embodiment, illustrated in Figure 4, one or both devices in the pair of devices may be placed on top of an appropriately doped layer 30 whose bandgap is so adapted that the high energy tail in the energy distribution of the photons of the light- emitting diode will be absorbed, in accordance with

Figure 5. The photoelectric cross-section for positive and negative charge barriers respectively in Fe-doped In P is highly energy-dependent, not least within the light-emitting diode range of 1.55-1.67 μm (correspond- ing to 0.74-0.80 eV) .

The principle is illustrated in Figure 5. As shown, the light emitted from the light-emitting diode has a dis¬ tribution with a high energy tail. The tail photons have a much greater tendency to generate charge carriers in the substrate than the more numerous photons, close to the emission peak. By placing in the vicinity of the light-emitting diode a photon filter 30 which will eliminate the part which is marked in black, the amount of photons detected will, admittedly, be reduced by a certain proportion, although the amount of charge carriers generated through photoelectric effect will, at the same time, be reduced by a much higher proportion, since at room temperature material of the type InP:Fe for instance, has a photo ionization cross-section which (for positive charge carriers) changes by more than two powers of ten over the relevant energy range.

Thus, the provision of at least one resistive channel results in a reduction in the voltage gradients that occur because of the unavoidable presence of charge carriers in the substrate. Furthermore, the provision of a filter between the light source (the pn-junction of the light-emitting diode) and the substrate will also reduce the supply of charge carriers in the substrate, which further improves against breakdown of the coupler. In view of the fact that the general principles and the conventional manufacturing methods of semi-conductors are well known, reference is made by way of example, with regard to material technology, to the monograph M. Razeghi: "The MOCVD Challenge: Volume 1: A Survey of GalnAsP-InP for Photonic and Electronic Applications" (Adam Hilger, Bristol, 1989) , and with particular refer¬ ence to the technology of light-emitting diodes, refer¬ ence is made to Gillessen-Schairer: "Light Emitting Diodes: An Introduction" (Prentice-Hall International, London, 1987) , these works being incorporated by reference in the present disclosure.

As will be understood by those skilled in this art, variations are possible within the scope of the inven¬ tion. Although the InP-material is preferred at present, it is also possible to work with GaAs, which has similar properties with regard to light conduction and refrac¬ tive index, or, e.g., GaP in the event that a semi- isolating GaP-substrate will be made available. It is also possible to arrange several pairs of light-emitting diodes and photo-diodes on one and the same substrate.

Claims

Claims
1. A monolithic optocoupler which comprises a light- emitting diode and a light detector arranged mutually spaced on the surface of a substrate, said substrate comprising a semi-conductor material having an intrinsic
6 8 conduction of 10 -10 ohmcm and being transparent to radiation emitted by the light-emitting diode, c h a r a c t e r i z e d by a resistive channel (7) disposed between the light-emitting diode (2) and the light detector (3) .
2. A monolithic optocoupler according to Claim 1, c h a r a c t e r i z e d in that the resistive channel includes at least one doped, preferably ion-implanted surface part (7) , which extends over the surface of the substrate between the light-emitting diode (2) and the light detector (3) .
3. A monolithic optocoupler according to Claim 1, c h a r a c t e r i z e d in that the substrate is comprised of indium phosphide.
4. A monolithic optocoupler according to Claim 1, c h a r a c t e r i z e d in that the substrate is comprised of gallium arsenide.
5. A monolithic optocoupler according to Claim 2, c h a r a c t e r i z e d in that a plurality of re¬ sistive channels (7) are disposed between the light- emitting diode and the light detector in the form of approximately 10 μm wide bands, implanted with helium
14 2 ons to a number of about 10 per cm .
6. A monolithic optocoupler according to Claim 1, c h a r a c t e r i z e d in that the light-emitting diode is placed on top of an epitactic protective layer (30) laid on the substrate; and in that the protective layer has a bandgap which corresponds to the energy of a high energy part of the light emitted from the light- emitting diode and which is smaller than the bandgap of the substrate material.
7. A monolithic optocoupler according to Claim 1, c h a r a c t e r i z e d in that when measured between the light-emitting diode and the light detector, the resistance is at least 100 Mohm and the breakdown voltage between the light-emitting diode and the light detector exceeds 4 kV.
PCT/SE1992/000580 1991-10-01 1992-08-24 A monolithic optocoupler WO1993007647A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
SE9102844A SE469204B (en) 1991-10-01 1991-10-01 monolithic optocoupler
SE9102844-9 1991-10-01

Publications (1)

Publication Number Publication Date
WO1993007647A1 true WO1993007647A1 (en) 1993-04-15

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AU (1) AU2697592A (en)
SE (1) SE469204B (en)
WO (1) WO1993007647A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2344455A (en) * 1998-12-01 2000-06-07 Mitel Semiconductor Ab Semiconductor device with low parasitic capacitance
WO2005076375A1 (en) * 2004-02-05 2005-08-18 Otkrytoe Aktsionernoe Obschestvo 'nauchno-Issledovatelsky Institut Girikond' Photoluminescent radiator, semiconductor photocell and octron based thereon
RU2642132C1 (en) * 2016-07-20 2018-01-24 Федеральное Государственное Бюджетное Образовательное Учреждение Высшего Образования "Новосибирский Государственный Технический Университет" Optoelectronic device

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3881113A (en) * 1973-12-26 1975-04-29 Ibm Integrated optically coupled light emitter and sensor
US4021834A (en) * 1975-12-31 1977-05-03 The United States Of America As Represented By The Secretary Of The Army Radiation-resistant integrated optical signal communicating device
US4275404A (en) * 1979-10-05 1981-06-23 Bell Telephone Laboratories, Incorporated Monolithic opto-isolator
EP0318883A1 (en) * 1987-12-02 1989-06-07 Asea Brown Boveri Ab Monolithic optocoupler

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3881113A (en) * 1973-12-26 1975-04-29 Ibm Integrated optically coupled light emitter and sensor
US4021834A (en) * 1975-12-31 1977-05-03 The United States Of America As Represented By The Secretary Of The Army Radiation-resistant integrated optical signal communicating device
US4275404A (en) * 1979-10-05 1981-06-23 Bell Telephone Laboratories, Incorporated Monolithic opto-isolator
EP0318883A1 (en) * 1987-12-02 1989-06-07 Asea Brown Boveri Ab Monolithic optocoupler

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2344455A (en) * 1998-12-01 2000-06-07 Mitel Semiconductor Ab Semiconductor device with low parasitic capacitance
US6287881B1 (en) 1998-12-01 2001-09-11 Mitel Semiconductor Ab Semiconductor device with low parasitic capacitance
WO2005076375A1 (en) * 2004-02-05 2005-08-18 Otkrytoe Aktsionernoe Obschestvo 'nauchno-Issledovatelsky Institut Girikond' Photoluminescent radiator, semiconductor photocell and octron based thereon
GB2426628A (en) * 2004-02-05 2006-11-29 Otkrytoe Aktsionernoe Obschest Photoluminescent radiator, semiconductor photocell and octron based thereon
GB2426628B (en) * 2004-02-05 2008-04-02 Otkrytoe Aktsionernoe Obschest Photoluminescent radiator, semiconductor photocell and optron based thereon
RU2642132C1 (en) * 2016-07-20 2018-01-24 Федеральное Государственное Бюджетное Образовательное Учреждение Высшего Образования "Новосибирский Государственный Технический Университет" Optoelectronic device

Also Published As

Publication number Publication date
SE9102844D0 (en) 1991-10-01
AU2697592A (en) 1993-05-03
SE9102844L (en) 1993-04-02
SE469204B (en) 1993-05-24

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