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Docket #: S20-443

Photonic transformer based on light-emitting diodes for DC voltage conversion

Stanford researchers in the Shanhui Fan Group have developed a new type of voltage converter capable of both AC and DC boost and buck operation. Utilizing a non-switching photonic mechanism, the voltage converter (hereafter referred to as a "photonic transformer") offers scalability across a wide range voltage ratios, supports high voltages, and provides excellent electrical isolation and Electro-Magnetic Interference (EMI) blocking, all within an extremely compact footprint with a substrate-transferrable thin-film profile.

The photonic transformer's basic design conceptually resembles a network of LEDs transferring energy to a network of Photo-Voltaic (PV) cells; however in the photonic transformer all of the LEDs and PV cells are monolithically integrated into a single thin-film device with one pair of input terminals and one pair of output terminals. The design utilizes a micron-scale high-index spacer to strongly couple the light-emitting and absorbing volumes, resulting in extremely high conversion efficiency. GaN-based implementations can achieve high output voltages with conversion efficiencies far above those of even today's best blue GaN-based LEDs. This near-unity power conversion efficiency furthermore eases thermal constraints to enable miniaturization of high-performance voltage converters while simultaneously improving electromagnetic compatibility and power quality for the systems they support.

Figure description - Figure description: Diagrammatic representation of a fully fabricated GaN-based photonic transformer (cross-sectional profile view). The emitting and absorbing GaN-based diode layers are grown serially, with the electrically-insulating, optically-transparent, nearly lattice-matched AlGaN layer grown between them. Next a sequence of patterned etch steps are performed which expose contact layers and separate the PV cells (and in some cases LEDs). A patterned layer of insulating SiO2 is subsequently deposited to electrically isolate the contact traces from the PV junctions' sidewalls. Finally contacts are deposited. Optional subsequent steps (not shown) include flip-chip bonding to a CMOS circuit die and substrate removal via laser lift-off.
Image credit: https://arxiv.org/abs/2103.14728

Stage of Development

  • Proof-of-concept completed. Photonic transformer constructed and physics validated via board-level implementation with discrete off-the-shelf LEDs and PV cells.
  • Proof-of-concept for monolithic implementation under development.

    • Applications

    • Generation of high DC voltages for Single-Photon Avalanche Detectors (SPADs) and SPAD arrays
      • May be particularly useful in space-constrained applications such as mobile consumer electronic devices with SPAD-array-based LIDAR
      • May be particularly useful in other "ultra-compact" SPAD-based LIDAR systems
    • DC voltage conversion on a variety of CMOS integrated circuits
      • May be particularly useful in SWAP-limited (Size, Weight, And Power) contexts
      • May be particularly useful where EMI from switching converters is undesirable or unacceptable
      • DC voltage conversion on flexible substrates including wearables
        • May be particularly useful for wearables charged by energy harvesting devices with low or inconsistent output voltages
        • DC-DC converters are used in numerous applications such as aerospace, consumer electronics, telecommunication, automotive, and medical

          • Advantages

          • As compared to existing transformers:
            • Miniature size - extremely small footprint compared with switching converters
            • Low noise - no switching noise at ouput, no EMI
            • Higher efficiency - much higher power conversion efficiency (approaching unity)
            • Less waste heat - loosens therma constraints on surrounding systems
            • High voltage and voltage conversion ratio
          • LED as compared to laser light sources:
            • Simpler and less expensive to fabricate since LED does not require a cavity
            • More robust operation - can operate with broader operational parameters
            • Higher ultimate efficiency

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