VTT Technical Research Centre of Finland Ltd. v. SiTime Corporation

CourtDistrict Court, N.D. California
DecidedJuly 9, 2020
Docket4:19-cv-01174
StatusUnknown

This text of VTT Technical Research Centre of Finland Ltd. v. SiTime Corporation (VTT Technical Research Centre of Finland Ltd. v. SiTime Corporation) is published on Counsel Stack Legal Research, covering District Court, N.D. California primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
VTT Technical Research Centre of Finland Ltd. v. SiTime Corporation, (N.D. Cal. 2020).

Opinion

1 2 3 4 5 UNITED STATES DISTRICT COURT 6 NORTHERN DISTRICT OF CALIFORNIA 7 8 VTT TECHNICAL RESEARCH CENTRE OF CASE NO. 4:19-cv-1174-YGR FINLAND LTD., 9 Plaintiff, CLAIM CONSTRUCTION ORDER 10 vs. Re: Dkt. Nos. 44, 45, 63 11 SITIME CORPORATION, 12 Defendant. 13

14 Plaintiff VTT Technical Research Centre of Finland Ltd. (“VTT”) brings this patent 15 infringement action against defendant SiTime Corporation (“SiTime”), alleging that SiTime 16 infringes U.S. Patent No. 8,558,643 (the “’643 Patent”), titled “Micromechanical Device Including 17 N-Type Doping for Providing Temperature Compensation and Method of Designing Thereof.” 18 Now before the Court are the parties’ claim construction disputes. 19 Having carefully considered the papers submitted, the parties’ arguments presented at the 20 claim construction hearing on May 15, 2020, and the pleadings in this action, and for the reasons 21 set forth below, the Court hereby adopts the constructions set forth herein. 22 I. BACKGROUND 23 The ’643 Patent is directed to temperature control of resonators (and other 24 micromechanical devices). (’643 Patent at 1:8-9.) Resonators are structures that vibrate (or 25 oscillate) at a precise frequency. (Dkt. No. 44-5 (“SiTime Prospectus”) at 2.) When combined 26 with another circuit that sustains the resonator’s vibration, the components form an oscillator that 27 can be used to provide clock signals in a system. (Id; Dkt. No. 45-5 (“Nguyen Decl.”) ¶ 17.) For 1 example, a computer might have oscillators to provide clock signals that synchronize the CPUs, 2 communication chips, and other components. (SiTime Prospectus at 2.) 3 Traditionally, resonators have been made out of quartz crystal. (Id. at 3.) However, quartz 4 crystal suffers from several limitations, including narrow frequency range, sensitivity to shock, 5 and limited programmability. (Id.) For this reason, electronics manufacturers have been trying to 6 replace quartz crystal with semiconductor-based “microelectromechanical systems” (MEMS). (Id. 7 at 1; ’643 Patent at 1:17-19.) MEMS resonators have greater programmability and may be 8 advantageously manufactured using scalable fabrication techniques. (’643 Patent at 1:15-19; 9 SiTime Prospectus at 3.) 10 One challenge preventing widespread adoption of MEMS resonators is “temperature drift.” 11 (’643 Patent at 1:19-22, 1:29-31.) In order to keep time accurately, resonators need to oscillate at 12 a stable frequency in the face of changing environmental conditions. (See SiTime Prospectus at 13 2.) Silicon-based resonators, however, have a resonance frequency that fluctuates due to ambient 14 temperature. (’643 Patent at 1:19-26.) Temperature drift stems from changes in material stiffness 15 as temperature increases. (Id. at 1:22-24.) When temperatures increase, silicon becomes less 16 “stiff” and thus vibrates at a lower frequency. (Id.; Nguyen Decl. ¶ 19.) 17 A known technique for reducing temperature drift involves “doping,” or adding an 18 impurity (“dopant”) to silicon. (See ’643 Patent at 1:61-2:2.) The prior art attempted to use n-type 19 (negative charge) and p-type (positive charge) dopants, as well as combined layers of p-doped and 20 n-doped materials, to reduce temperature drift. (Id. at 1:61-2:43; Nguyen Decl. ¶ 20.) However, 21 these techniques failed to achieve temperature compensation over sufficiently wide temperature 22 ranges. (’643 Patent at 2:47-48.) Moreover, the inventors of the ’643 Patent found that even at 23 optimal doping levels, constant doping concentration fails to achieve stable frequency. (Id. at 24 15:4-25, Figs. 16a-c.) 25 To improve the prior art, the ’643 Patent proposes a “novel temperature compensated 26 semiconductor structure whose temperature sensitivities can be managed . . . over a wide 27 temperature range.” (’643 Patent at 2:52-55.) The invention of the ’643 Patent lies in a MEMS 1 device that has a drive or sense means coupled to a resonator1 with “at least two regions having 2 different materials properties.” (Id. at claims 1, 29.) The material properties of the regions and 3 their relative volumes “define an effective material having the desired temperature compensation 4 characteristics.” (Id. at 2:63-66.) Specifically, each region comprises one or more n-type doping 5 agent, and the type of doping agent, its concentration, and the crystal orientation are “configured 6 so that the temperature sensitivities of the generalized stiffness are of opposite sign at least at one 7 temperature” for the regions. (Id. at 2:66-3:7, claim 1.) As a result of this configuration and the 8 relative volume, the overall temperature drift of the generalized stiffness is 50 ppm or less over 9 100 ℃. (Id. at claims 1, 29.) 10 The invention works as follows: when silicon is “doped” with another material, its 11 temperature sensitivity—the extent and direction in which its frequency or stiffness changes due to 12 temperature at a given point—changes. (See id. at 6:23-25, 15:4-9, Figs. 15a-c.) By adjusting 13 dopant types, concentrations, and crystal orientation, the regions can have opposite temperature 14 sensitivities, so that one region has increasing frequency as temperature increases while another 15 region has decreasing frequency. (Id. at 3:16-60, Figs. 2a-2b.) Additionally, by changing the 16 volume, the regions’ weight on the overall elasticity can be adjusted. (Id. at 12:44-67.) Thus, by 17 configuring these factors, the resonator can be designed so that the effects of temperature “cancel 18 out” among the regions and the overall temperature behavior of the composite material is the 19 weighted average of the constituents.2 (Id. at 6:23-33, 15:26-30, Fig. 2c.) In this way, an effective 20 material with low temperature drift can be achieved. (Id. at 15:20-25.) 21 Independent claim 1 recites:

23 1 The claims recite a “semiconductor element capable of resonating or deflecting,” which presumably includes, but is broader than, a resonator. (See ’643 Patent at claims 1, 29.) 24

2 The specification describes implementing the invention in a “superlattice” structure 25 where regions with different dopant concentrations are stacked. (’643 Patent at 4:1-15, 7:15- 11:50.) However, the specification makes clear that “other layer configurations can be used too, 26 provided that they form a coupled spring system and the slopes of the temperature sensitivities suitably match at each point of the desired temperature range.” (Id. at 12:25-30.) Even without a 27 lattice structure, “the general approach of cancelling positive/negative temperature coefficients (of 1 1. A micromechanical device comprising; a semiconductor element capable of deflecting or resonating and comprising at 2 least two regions having different material properties, 3 drive or sense means functionally coupled to said semiconductor element, 4 wherein 5 at least one of said regions comprises one or more n-type doping agents, 6 the relative volumes, doping concentrations, doping agents and/or crystal orientations of the regions being configured so that 7 the temperature sensitivities of the generalized stiffness are opposite 8 in sign at least at one temperature for the regions, and 9 the overall temperature drift of the generalized stiffness of the semiconductor element is 50 ppm or less on a temperature range of 10 100° C. Independent claim 29 recites: a 12 29. A method for designing a micromechanical device comprising 13 . . a semiconductor element capable of deflecting or resonating and comprising at 14 least two regions having different material properties,

45 drive or sense means functionally coupled to said semiconductor element,

“i A 16 the method comprising 7 choosing a basic semiconductor material for the semiconductor element,

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VTT Technical Research Centre of Finland Ltd. v. SiTime Corporation, Counsel Stack Legal Research, https://law.counselstack.com/opinion/vtt-technical-research-centre-of-finland-ltd-v-sitime-corporation-cand-2020.