Strontium scandium borate (Sr2Sc2B4O11) halogen-free redistribution-layer dielectric

Strontium scandium borate (Sr2Sc2B4O11) is a halogen-free, alkaline-earth/rare-earth borate glass-ceramic engineered as a redistribution-layer (RDL) dielectric for advanced semiconductor packaging. Its core value proposition is straightforward: it offers an inorganic, PFAS-free, halogen-free alternative to the polymer-based dielectrics that currently dominate back-end-of-line (BEOL) and panel-level RDL stacks, at a bandgap of approximately 4.47 eV that situates it well above the leakage threshold required for low-power, high-frequency packaging applications. Regulatory pressure on halogenated compounds — including brominated flame retardants embedded in dielectric laminates — is tightening globally, and OSATs (outsourced semiconductor assembly and test houses) are under documented procurement pressure to qualify replacement materials before mandated phase-outs arrive. This asset is a dependent embodiment within the broader patent family covering halogen-free alkaline-earth/rare-earth borate RDL dielectrics. Its role in the portfolio is that of a backup or fallback claim: if the primary genus claim faces prior-art narrowing, Sr2Sc2B4O11 provides a specifically reduced-to-practice species with confirmed structural relaxation, a characterized bandgap, and a defined crystal system (triclinic P-1). The asset is held honestly — the full phonon stability picture has one open validation gate, described in detail below — and it is claimed accordingly in dependent rather than independent form, pending DFT phonon refinement to resolve a residual zone-boundary soft mode. That posture is scientifically responsible and legally prudent; it also means a buyer or licensee knows exactly what additional work closes the gap to a fully confirmed, independently stable composition.

Each candidate is validated by multiple independent machine-learning interatomic potentials. A material advances only when the engines agree on phonon (dynamic) stability — disagreement is surfaced, not hidden.

Sr2Sc2B4O11 adopts the triclinic space group P-1, a low-symmetry crystal system typical of complex borate networks where corner- and edge-sharing BO3/BO4 polyhedra interleave with alkaline-earth (Sr²⁺) and rare-earth (Sc³⁺) coordination environments. The P-1 symmetry imposes no constraint on polyhedral tilt angles, which gives the borate network substantial structural flexibility and is characteristic of compositions that transition readily between crystalline and glass-ceramic microstructural states — a property that matters practically for thin-film deposition routes such as spin-on glass, ALD-seeded CVD, or sol-gel processes. The computed bandgap of approximately 4.47 eV places the material solidly in the wide-gap insulator regime, well above the ~3.5 eV threshold at which leakage currents become problematic for fine-pitch RDL applications operating at sub-1 V node voltages. Loss tangent is estimated in the 1×10⁻³ to 1×10⁻² range, consistent with borate glass-ceramics of similar composition, though this remains an open bench measurement rather than a DFT-derived value. The computational validation workflow applied three independent machine-learning interatomic potentials — MACE, CHGNet, and MatterSim — in a staged protocol. In the first stage (structural relaxation), all three potentials independently converged to the same energy-minimized geometry, establishing that the P-1 crystal structure is a true local minimum on the potential-energy surface under all three force fields. This 3-of-3 relaxation consensus is a meaningful positive signal: it rules out force-field-specific artifacts in the ground-state geometry and confirms the formula unit and space group are correctly assigned. In the second stage (phonon analysis), the picture becomes more nuanced. MACE finds the structure phonon-stable at the Gamma point with no imaginary modes. CHGNet and MatterSim, however, each identify a residual soft mode at the zone boundary, with a small imaginary frequency of approximately −0.19 THz. This is a majority-stable verdict: two out of three potentials flag a potential instability at a wavevector away from Gamma, while one does not. The magnitude of the soft mode is small but non-trivial, and the discrepancy between potentials is exactly the kind of ambiguity that DFT phonon calculations are designed to resolve. The practical implication is clear. Zone-boundary soft modes at this magnitude can arise from two distinct physical causes: a genuine structural instability that would manifest as a displacive phase transition or decomposition pathway under synthesis conditions, or a force-field training artifact in which one or two potentials slightly underestimate the restoring force at a particular high-symmetry wavevector. DFT phonon calculations — specifically, density-functional perturbation theory (DFPT) on the relaxed supercell — would distinguish these cases unambiguously. A DFT-confirmed absence of imaginary modes would elevate this composition to the same fully validated tier as the leading members of the borate family; a DFT-confirmed instability would clarify whether distortion to a lower-symmetry polymorph resolves the issue or whether the composition is a genuine dead end. In either case, the information has direct value: positive confirmation strengthens the dependent claim and the overall family; negative confirmation adds a high-quality labeled negative result to Lattice Graph's atlas of failed experiments, which has independent value for training next-generation MLIP models and for documenting prior art that competitors cannot subsequently claim. This honest posture about open validation gates is a feature of the research methodology, not a deficiency. The broader genus covered by the patent family — A₂RE₂B₄O₁₁ where A is Sr, Ca, or Ba and RE is Sc, Y, or Lu, plus the LaBO₃ orthoborate sub-genus — encompasses a substantial compositional landscape. Sr2Sc2B4O11 was selected as a specific species because strontium and scandium occupy a favorable size and charge-matching window: Sr²⁺ provides a large alkaline-earth site that stabilizes the borate network against collapse, while Sc³⁺ is the smallest trivalent rare-earth ion, promoting denser, more thermally stable coordination. This combination is known from glass science to suppress crystallization exotherms at moderate temperatures, a property that matters for back-end-of-line processing where thermal budgets above approximately 400°C are incompatible with copper interconnects. The dielectric stack context — integration into a redistribution layer between chiplets or between die and substrate — also imposes requirements on coefficient of thermal expansion (CTE) matching and adhesion to copper seed layers, both of which are achievable targets for borate glass-ceramics but remain to be characterized experimentally for this specific composition.

The addressable market for this asset is the advanced packaging RDL dielectric segment, which sits within the broader advanced semiconductor packaging materials market. Redistribution layers are the fine-pitch interconnect layers — patterned by lithography, not wire bonding — that route signals between chiplet pads, between die and substrate, or between interposer layers in 2.5D/3D integrated packaging architectures. Dielectric materials integrated into RDL stacks must simultaneously satisfy low loss tangent, adequate breakdown strength, process compatibility with copper damascene or semi-additive processing (SAP), and increasingly stringent environmental compliance requirements. The total addressable market for halogen-free inorganic RDL dielectrics specifically is estimated at $0.2 to 0.5 billion USD — a focused niche, not a broad materials market, reflecting the reality that RDL dielectrics compete on performance and regulatory posture rather than volume commodity pricing. The buying audience is concentrated: advanced-packaging OSATs — companies such as those operating fan-out wafer-level packaging or panel-level packaging lines — are the primary customers. These organizations are under direct pressure from their OEM customers (hyperscalers, mobile SoC vendors, HPC chipmakers) to demonstrate halogen-free supply chains ahead of anticipated regulatory updates to IEC 61249-2-21 and analogous standards. A second, smaller segment is IDMs and foundries operating their own advanced packaging lines, who similarly need to qualify backup dielectric materials before their current halogenated polymer suppliers face phase-out mandates. Licensing logic for this asset would most naturally take the form of a per-wafer or per-panel royalty bundled with process know-how transfer, or alternatively a lump-sum license to a glass-ceramic supplier who then qualifies the material for sale into the OSAT market. Given the niche TAM, the monetization path is more likely a strategic license to one or two players seeking freedom-to-operate in the halogen-free RDL space than a broad royalty program.

halogen-free borate RDL dielectric option

halogen-free package-integrated RDL form; dependent relaxation-converged posture pending DFT phonon

The most natural acquirers or licensees for this asset are advanced-packaging OSATs operating fan-out wafer-level or panel-level packaging lines and currently qualifying replacement materials for halogenated polymer dielectrics. These companies have both the motivation — regulatory compliance timelines — and the process infrastructure to take a glass-ceramic composition from laboratory characterization through OSAT-level qualification. A secondary acquirer profile is specialty glass and glass-ceramic manufacturers (producers of LTCC substrates, optical coating materials, or electronic-grade borosilicate glasses) who would value the composition IP as a defensive position or as an entry point into the semiconductor packaging materials market, where margins are substantially higher than in traditional glass markets. Strategic fit also exists for IDMs or foundries building proprietary advanced packaging capabilities in-house, for whom owning the dielectric composition IP alongside the process IP reduces dependence on external material suppliers. In a licensing scenario, a glass-ceramic material supplier who obtains a license could offer qualified Sr2Sc2B4O11 feedstock or precursor solutions to multiple OSAT customers, making the royalty economics per transaction modest but the addressable customer base broader. The asset's value is highest when bundled with the broader A₂RE₂B₄O₁₁ family claim and with the process know-how for low-temperature glass-ceramic crystallization, since the composition alone without deposition process guidance leaves a substantial engineering gap for any acquirer to bridge independently.

The most immediate technical risk is the unresolved zone-boundary soft mode. If DFT phonon refinement confirms a genuine instability, the P-1 structure of Sr2Sc2B4O11 may undergo a displacive distortion under synthesis or annealing conditions, potentially altering the dielectric properties or complicating microstructural control in thin-film form. This risk is bounded: the magnitude of the soft mode (−0.19 THz) is small, and the most likely outcome of a confirmed instability is a distortion to a closely related lower-symmetry polymorph that retains the borate network topology and most of the electronic properties. The DFT calculation needed to determine this is a standard, low-cost computational task, and Lattice Graph's workflow is set up to execute it. The second technical risk is the loss-tangent uncertainty: a measured value at the upper end of the estimated range would make the composition a marginal rather than competitive dielectric at millimeter-wave frequencies, which would limit the addressable customer base to lower-frequency packaging applications where polymer dielectrics already perform adequately. The commercial risk is primarily one of timing and process development. The RDL dielectric market is not waiting for inorganic alternatives — OSATs have near-term qualification pipelines built around improved polymer formulations, and displacing an incumbent process material requires not just a better material but a fully qualified deposition, patterning, and reliability test package. The path to de-risking is sequential and well-defined: DFT phonon confirmation first (2–4 weeks of compute), followed by synthesis of a test specimen and loss-tangent measurement (1–3 months in a ceramics lab), followed by thin-film deposition trials at reduced temperature to confirm BEOL compatibility. Each step is a go/no-go gate that either advances the asset toward commercialization or, if negative, provides high-quality experimental data that enriches the portfolio's negative-result atlas and informs the next candidate in the A₂RE₂B₄O₁₁ series.