Composite-copper, low-thermal-resistance heat sinks for laser-diode bars, mini-bars and single-emitter devices

Here we present characteristic performance of laser-diode devices employing a novel CTE-matched heatsink technology (where CTE is Coefficient of Thermal Expansion). Design variants of the composite-copper platforms include form-fit-compatible versions of production CS (for standard 1-cm-wide bars) and CT (for single-emitter devices and mini-bars) assemblies. Both employ single-step AuSn bonding and offer superior thermal performance to that of current production standards. These attributes are critical to reliability at high powers in both CW and hard-pulse (e.g., 1sec on/1sec off) operation. The superior thermal performance of the composite-copper CS device has been verified in CW testing of bars where 85W is typically obtained at 95A (compared to 76W from production-standard, indium-bonded, solid-copper CS devices). This result is especially significant as alternative CTE-matched bar platforms (e.g., those employing a sub-mount bonded to a solid copper heatsink) typically compromise the effective thermal resistance in order to achieve the CTE match (and often require two-step bonding). The close CTE match of the composite-copper CS results in relatively narrow, single-peaked spectra. Initial step stress tests of eight devices in hard-pulse operation up to 80A has been completed with no observed failures. Six of these devices have subsequently been operated in hard-pulse mode at 55A for >4000 with no failures. The CT variant of the composite-copper heatsink is predicted to offer a reduction in thermal resistance of nearly 30% for a 5-emitter mini-bar (500-μm pitch). In first-article testing, the maximum achievable CW power increased from 20W (standard CuW CT) to 24W (composite-copper CT). As with the CS devices, the composite-copper CT assemblies exhibited characteristically narrower spectral profiles.