Rothschild v. Cree Inc
| Decision Date | 13 May 2010 |
| Docket Number | Civil Action No. 10-10133-WGY. |
| Citation | 711 F.Supp.2d 173 |
| Parties | Gertrude Neumark ROTHSCHILD, Plaintiff,v.CREE, INC., Defendant. |
| Court | U.S. District Court — District of Massachusetts |
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Gerard F. Diebner, Albert Lionel Jacobs, Albert Jacobs LLP, Daniel Allen Ladow, Jeffrey C. Morgan, Troutman Sanders LLP, New York, NY, for Plaintiff.
Thomas C. Frongillo, Weil, Gotshal & Manges LLP, Boston, MA, Matthew Powers, Weil, Gotshal & Manges LLP, Redwood Shores, CA, for Defendant.
I. INTRODUCTION
In the present case, the plaintiff Gertrude Neumark Rothschild charges the defendant Cree, Inc. with infringement of her U.S. Patents Nos. 4,904,618 (the “'618 Patent”) and 5,252,499 (the “'499 patent”). This memorandum and order addresses various motions brought by the parties, including a motion to dismiss for lack of standing, motions for claim construction, and motions for summary judgment.
II. BACKGROUNDA. Facts
Rothschild owns two patents on methods of producing light emitting diodes (“LEDs”), which are at issue in this case:
The '618 Patent, entitled Process for Doping Crystals of Wide Band Gap Semiconductors, issued February 27, 1990, on an application filed August 22, 1988; and
the '499 Patent, entitled Wide Band Gap Semiconductors Having Low Bipolar Resistivity and Method of Formation, issued October 12, 1993, on an application filed August 15, 1988.
LEDs are used in a number of electronic devices ranging from display panels to billboards and even traffic lights. From a technological standpoint, LEDs are essentially p-n (positive-negative) junctions of wide band gap semiconductor materials. A semiconductor, as the name implies, is a material whose electrical conductivity is in the intermediate range between insulators and conductors. This means semiconductor material can conduct electricity under certain conditions, but not others. This characteristic makes the semiconductor a good medium for the control of electrical current.
The semiconductors used to form the p-n junctions of LEDs are crystalline solids. The crystalline solid is a crystal lattice consisting of two types of atoms. Semiconductors can be made from either of two types of materials (1) a II-VI compound or (2) a III-V compound. To understand their differences, consider the periodic table of elements. The periodic table is arranged such that elements with similar properties fall into the same columns or groups. When an element from Group II of the periodic table, such as zinc (“Zn”) or cadmium (“Cd”), having two electrons in its outer shell, is combined with an element from Group VI, such as selenium (“Se”) or tellurium (“Te”), having six electrons in its outer shell, a compound having a normal eight electrons in its outer shell, such as zinc selenide (“ZnSe”), is formed. A crystal lattice consisting of a Group II element and a Group IV element is chemically stable. This type of compound is called a II-VI compound. Likewise, a semiconductor may be formed by combining an element from Group III, such as gallium (“Ga”), having three electrons in its outer shell, with an element from Group V, such as arsenic (“As”), having five electrons in its outer shell. Again, this compound is also chemically stable. This type of compound is called a III-V compound.
Doping is the process of intentionally introducing impurities into a semiconductor material (II-VI compound or III-V compound) to change its electrical properties. Likewise, a “dopant,” as defined in Rothschild v. Cree, Inc., No. 05-5939, 2007 WL 1314619 (“ Rothschild I ”),1 “means an impurity added to a semiconductor material to alter its electronic properties.” Rothschild I at *3. If a dopant is incorporated into a semiconductor material, either during or after crystal growth, the electrical properties of the material may be changed in a useful manner. For example, if a II-VI compound such as ZnSe is doped with an element from Group V of the periodic table, such as nitrogen (“N”), having five electrons in its outer shell, the N atoms displace some of the Se atoms in the crystal lattice, thereby creating electron acceptors or “holes” in the crystal, making it a “p-type” material. Essentially, atoms with five electrons in their outer shell are introduced into the crystal and replace some of the existing atoms in the crystal lattice with six electrons in their outer shell. The result is that there is a deficit of electrons, and since compounds strive to have eight electrons in their outer shell, the compound wishes to accept electrons. Conversely, if the dopant is an element from Group III, such as Ga, having three electrons in its outer shell, its atoms displace some of the Zn atoms in the lattice, creating an excess of electrons in the crystal, making it an “n-type” material. Essentially, atoms with three electrons in their outer shell are introduced into the crystal and replace some of the existing atoms in the crystal lattice with two electrons in their outer shell. The result is that there is a surplus of electrons, and since compounds strive to have eight electrons in their outer shell, the compound desires to lose electrons.
A p-n junction consists of an n-type semiconductor at one end, a gap, and a p-type semiconductor at the other end. When a voltage is applied across the junction, electrons will move from the n-type material to fill the holes in the p-type material (flowing from negative to positive). As the electrons jump across the gap, the energy they lose in dropping from the conduction band (n-type material) to the valence band (p-type material) is released in the form of light. The wavelength or color of the light depends on the width of the gap between those bands in the particular material. For example, if the band gap is between 1.65 and 2.00 electron volts (“eV”), red light is produced; if it is below 1.65 eV, invisible infrared light or heat is produced. If the band gap is between 2.51 and 2.76 eV, blue light is produced; if it is above that range, violet or ultraviolet light is produced.
Semiconductor materials with wide band gaps are more difficult to dope because they more readily become “compensated.” To understand the concept of compensation, it is important to realize that, in practice, semiconductor materials contain internal impurities even before other impurities are introduced externally via doping. Compensation refers to the phenomenon in which impurities in the material itself supply the electrons to fill the holes in p-type material or supply the acceptors to receive the electrons in n-type material. In other words, if these internal impurities can satisfy the electro-chemical needs of the n-type or p-type semiconductor material, it is no longer necessary to incorporate the external dopants. Hence, the occurrence of compensation reduces the incorporation of the dopants into the crystal lattice and thereby increases the resistivity of the semiconductor. When there is high resistivity, electrons have difficulty jumping across the gap in the p-n junction, especially when it is very wide. This phenomenon explains why red LEDs (with narrow band gaps) were much more easily produced and more commonly used than blue LEDs (with wide band gaps), which have been called the long-sought Holy Grail of LED technology.
The Abstract of the '618 Patent describes the invention as follows:
Non-equilibrium impurity incorporation is used to dope hard-to-dope crystals of wide band gap semiconductors, such as zinc selenide and zinc telluride. This involves incorporating into the crystal a compensating pair of primary and secondary dopants, thereby to increase the solubility of either dopant alone in the crystals. Thereafter, the secondary more mobile dopant is removed preferentially, leaving the primary dopant predominant. This technique is used to dope zinc selenide p-type by the use of nitrogen as the primary dopant and lithium as the secondary dopant.
'618 Patent.
Rothschild charges Cree with infringement of Claims 1, 4, and 5 of the '618 Patent. Claims 1 and 5 are the only independent claims of the patent. Claim 1 reads:
1. A process for the non-equilibrium incorporation of a dopant into a crystal of a wide band gap semiconductor comprising the steps of treating the crystal in the presence of first and second compensating dopants of different mobilities for introducing substantially equal amounts of the two dopants into at least a portion of the crystal such that the concentration of the less mobile of the two dopants in said portion of the crystal is in excess of the solubility therein of the less mobile dopant in the absence of the more mobile of the two dopants, and then heating the crystal to remove therefrom preferentially the more mobile of the two dopants whereby there is left a non-equilibrium concentration of the less mobile dopant in said portion of the crystal.
'618 Patent col.5 ll.11-24.
Claim 5 reads:
5. The process of forming a p-n junction diode in a crystal of a wide band gap semiconductor comprising the steps of preparing a crystal of the semiconductor of one conductivity type and growing on a surface of the crystal an epitaxial layer that includes a compensating pair of primary and secondary dopants in substantially equal amounts, such that the concentration of the primary dopant in the layer is in excess of the solubility of the primary dopant in the layer in the absence of the secondary dopant, where the primary dopant is characteristic of the conductivity type opposite that of said crystal and is less mobile than the secondary dopant,...
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