[Paper Review] Thermal Transient Characterization of Packaged Thin Film Microcoolers

Kazuhiko Fukutani, Reena Singh+1 more|ArXiv.org|Sep 12, 2007

Thermal properties of materials9 references3 citations

TL;DR

This study applies network identification by deconvolution (NID) to thermally transient responses of packaged and unpackaged thin film microcoolers, using a coplanar probe system with ~100 ns time resolution to isolate thermal resistances of individual layers. The method successfully extracts buffer layer and silicon substrate resistances consistent with theory, while highlighting the need for faster transient response to resolve superlattice thermal resistance from underlying SiNx layers.

ABSTRACT

A network identification by deconvolution (NID) method is applied to the thermal transient response of packaged and unpackaged microcoolers. A thin film resistor on top of the device is used as the heat source and the temperature sensor. The package and the bonding thermal resistances can be easily identified by comparing structure functions. High-speed coplanar probes are used to achieve a short time resolution of roughly 100ns in the transient temperature response. This is used to separate the thermal properties of the thin film from the substrate. The obtained thermal resistances of the buffer layer and Silicon substrate are consistent with the theoretical calculations. In order to estimate the superlattice thermal resistance and separate it from the thin SiNx layer deposited underneath the thin film resistive sensor, an order of magnitude faster thermal transient response is needed.

Motivation & Objective

• To characterize the thermal transient response of packaged thin film microcoolers with high temporal resolution.
• To isolate and quantify individual thermal resistances in the multilayer structure, including the buffer layer and silicon substrate.
• To assess the limitations of current measurement resolution in resolving the thermal resistance of superlattice structures.
• To compare measured thermal resistances with theoretical predictions for validation.
• To identify the need for faster transient response to distinguish between closely spaced thermal layers such as superlattices and underlying SiNx.

Proposed method

• A thin film resistor serves as both the heat source and temperature sensor on the microcooler surface.
• High-speed coplanar probes achieve a time resolution of approximately 100 ns for transient temperature measurements.
• Network identification by deconvolution (NID) is applied to extract thermal network parameters from the transient response.
• Structure functions are compared between packaged and unpackaged devices to identify package and bonding thermal resistances.
• Theoretical thermal resistances of the buffer layer and silicon substrate are calculated and used for validation.
• The method enables separation of thermal properties of the thin film from the substrate through time-domain analysis.

Experimental results

Research questions

• RQ1 What is the contribution of the package and bonding layers to the overall thermal resistance in packaged microcoolers?
• RQ2 How accurately can the thermal resistances of the buffer layer and silicon substrate be extracted using transient response data?
• RQ3 Can the NID method resolve the thermal resistance of the superlattice structure from the underlying SiNx layer with current time resolution?
• RQ4 How do measured thermal resistances compare to theoretical predictions for the buffer layer and substrate?
• RQ5 What level of time resolution is required to resolve the thermal resistance of a superlattice structure adjacent to a SiNx layer?

Key findings

• The thermal resistance of the buffer layer and silicon substrate, as measured by the NID method, shows good agreement with theoretical calculations.
• The package and bonding thermal resistances were successfully identified through comparison of structure functions from packaged and unpackaged devices.
• The 100 ns time resolution enabled effective separation of thermal properties between the thin film and the substrate.
• The method revealed that current measurement speed is insufficient to resolve the thermal resistance of the superlattice from the underlying SiNx layer.
• An order of magnitude faster transient response is required to achieve the necessary resolution for distinguishing the superlattice thermal resistance.