Room Temperature Liquid Metal Research Articles

Liquid–Metal Vertical Interconnects for Flip Chip Assembly of GaAs C-Band Power Amplifiers Onto Micro-Rectangular Coaxial Transmission Lines

Prior work has demonstrated a new process utilizing room-temperature liquid metal, Galinstan, as an interconnect material for flip-chip bonding. This interconnect forms a flexible bond between chips and carriers, and, therefore, a flip-chip assembly using this technology is much less susceptible to thermomechanical stresses. This paper applies this concept to interconnect GaAs MMIC chips to 3-D Polystrata transmission-line structures. Passive assemblies are utilized to model, test, and verify liquid-metal interconnections, giving average losses per liquid-metal transition of about 0.11 dB out to 26.5 GHz, low parasitics per transition, and demonstrated reliability after temperature cycling. A prefabricated GaAs MMIC chip is postprocessed for liquid-metal assembly. Measured results show, over the MMIC's 4.9-8.5-GHz frequency range, the system's overall reduction in gain of the MMIC is 1.4 dB or 0.7 dB per RF transition as compared with direct probing of the MMIC chip.

Direct Writing of Flexible Electronics through Room Temperature Liquid Metal Ink

BackgroundConventional approaches of making a flexible circuit are generally complex, environment unfriendly, time and energy consuming, and thus expensive. Here, we describe for the first time the method of using high-performance GaIn10-based electrical ink, a significantly neglected room temperature liquid metal, as both electrical conductors and interconnects, for directly writing flexible electronics via a rather easy going and cost effective way.MethodsThe new generation electric ink was made and its wettability with various materials was modified to be easily written on a group of either soft or rigid substrates such as epoxy resin board, glass, plastic, silica gel, paper, cotton, textiles, cloth and fiber etc. Conceptual experiments were performed to demonstrate and evaluate the capability of directly writing the electrical circuits via the invented metal ink. Mechanisms involved were interpreted through a series of fundamental measurements.ResultsThe electrical resistivity of the fluid like GaIn10-based material was measured as 34.5 µΩ·cm at 297 K by four point probe method and increased with addition of the oxygen quantity, which indicates it as an excellent metal ink. The conductive line can be written with features that are approximately 10 µm thick. Several functional devices such as a light emitting diode (LED) array showing designed lighting patterns and electrical fan were made to work by directly writing the liquid metal on the specific flexible substrates. And satisfactory performances were obtained.ConclusionsThe present method opens the way to directly and quickly writing flexible electronics which can be as simple as signing a name or drawing a picture on the paper. The unique merit of the GaIn10-based liquid metal ink lies in its low melting temperature, well controlled wettability, high electrical conductivity and good biocompability. The new electronics writing strategy and basic principle has generalized purpose and can be extended to more industrial areas, even daily life.

Heat Spreader Based on Room-Temperature Liquid Metal

This study reports a high-performance heat spreader based on room-temperature liquid metal coolant. Conceptual cooling experiments show that liquid metal heat spreader owns particularly excellent heat spreading performance. In order to evaluate the driving features of liquid metal, a miniaturized electromagnetic pump with high reliability and low power consumption was fabricated and tested. Extreme experiments were performed and showed that liquid metal heat spreader could overwhelm all the latest typical advanced spreading technologies and serve as an ultimate heat spreading solution under extremely high heat flux density condition.

Numerical calibration of a Lorentz force flowmeter

Numerical simulation of complex-shaped devices for contactless electromagnetic flow measurement in metallurgy is a challenge for computational magnetohydrodynamics. We report a series of numerical simulations which demonstrate for the first time that it is possible to predict the calibration constant of a generic Lorentz force flowmeter (LFF) with an uncertainty close to the requirements of real-life industrial applications. Our simulations involve both magnetostatic computations of a complex-shaped magnet system and magnetohydrodynamic computations of the flow of a liquid metal in a nozzle under the influence of a predominantly transverse magnetic field. In order to assess the role of turbulence, the simulations have been performed both for laminar and for turbulent flows using Reynolds-averaged Navier–Stokes equations in the latter case. In addition to the numerical simulations we have measured the calibration constant of the considered LFF using room-temperature liquid metal instead of liquid aluminum. A comparison between the numerically predicted and the measured values of the calibration constant shows that they differ by only 3.4%. This result suggests that numerical calibration of a LFF may become an economic alternative to expensive full-scale experimental calibration.

An experimental investigation of liquid metal thermal joint

This paper presents a highly flexible thermal joint based on room-temperature liquid metal. With the liquid metal joint, a flexible heat conduction device could be fabricated and operate efficiently under bending, torsion or vibration conditions. Conceptual experiments demonstrated that the tolerable bending and torsion angle could be as large as 120°, and the heat transfer capability would not decrease under the vibration frequency of 1–5 Hz. In order to minimize the mechanism, a miniature electromagnetic pump with high efficiency was fabricated and integrated. Both the thermal resistance distribution and pump power were evaluated. The results showed that flexible liquid metal thermal joint owned high heat transfer capability, low power consumption, and could serve as an attractive dynamic heat conduction solution for military and civilian use.

Self-Driven Electronic Cooling Based on Thermosyphon Effect of Room Temperature Liquid Metal

Thermal management has been a critical issue for the safe running of an electronic device. Driving liquid metal with low melting point to extract heat from the thermal source is highly efficient because of its superior thermophysical properties over conventional coolant such as water or the like. In this paper, utilizing thermosyphon effect to drive room temperature liquid metal for electronic cooling was proposed for the first time with its technical feasibility demonstrated. This may lead to a self supported cooling which just utilizes the waste heat produced by the hot chip to drive the flow of liquid metal. And the device thus fabricated will be the one without any external pump and moving elements inside. A series of conceptual experiments under different operational conditions were performed to evaluate the cooling performance of the new method. Meanwhile, the results were also compared with that of water cooling by ways of thermal infrared graph and temperatures acquired by thermocouples. According to the measurements, it was found that the cooling performance of liquid metal was much stronger than that of water, and this will become even better with the increase of heat load, and height difference between the cooler and heater. A theoretical thermal resistance model was established and convective heat transfer coefficient was calculated to interpret the phenomenon with uncertainty analyzed. With further improvement of the present system and liquid metal coolant, this method is expected to be flexibly useful for heat dissipation of light-emitting diode (LED) street lamp, desk computer and radio remote unit (RRU), where confined space, efficient cooling, low energy consumption, dust-proof and water-proof are critically requested.

Harvesting low grade heat to generate electricity with thermosyphon effect of room temperature liquid metal

Based on thermosyphon effect of room temperature liquid metal, a technical strategy of harvesting low grade heat to generate electricity was proposed. A conceptual system was constructed and an open circuit voltage of 2.62 V with an electrical output power of 110 mW was yielded when the heating power was 45.6 W. This method resolves the difficulty of installing an electric generator in confined space and significantly enlarges the area for converting heat to electricity. Due to its simplicity, avoidance of moving parts, wide working temperature range, and self powering feature, this electric generation system is extremely reliable, completely silent, and flexible.

Liquid metal stretchable unbalanced loop antenna

We present a 2.4 GHz unbalanced loop antenna that can be stretched along multiple dimensions simultaneously. It was realized by incorporating room temperature liquid metal alloy into microstructured channels in an elastic material. The demonstrated prototype exhibits a stretchability of up to 40% along two orthogonal orientations as well as foldability and twistability. Port impedance and radiation characteristics of the nonstretched and stretched antenna were studied numerically and experimentally. Measured results indicate a radiation efficiency of more than 80%.

Foldable and Stretchable Liquid Metal Planar Inverted Cone Antenna

A mechanically flexible planar inverted cone antenna (PICA) for ultrawideband (UWB) applications is presented. It can be both folded and stretched significantly without permanent damage or loss of electrical functionality. The antenna is manufactured with a process in which conductors are realized by injecting room temperature liquid metal alloy into micro-structured channels in an elastic dielectric material. The elastic dielectric material together with the liquid metal enables bending with a very small radius, twisting, and stretching along any direction. Port impedance and radiation characteristics of the non-stretched and stretched antenna are studied in simulations and experiments. The presented antenna has a return loss better than 10 dB within 3-11 GHz and a radiation efficiency of > 70% over 3-10 GHz, also when stretched. Tests verify that stretching up to 40% is possible with maintained electrical performance. The presented antenna is useful for example for body-worn antennas and in applications in harsh environments where mechanical flexibility helps improve durability.