Search

We introduce a noncontact experiment method to estimate thermal conductivity of nanoscale thin films by fitting high spatial resolution thermoreflectance images of surface spot heating to a finite element simulated temperature distribution. The thin-film top surface is heated by a 1 μ m diameter focused, 825 nm wavelength laser spot. The surface temperature distribution in the excited sample is imaged by thermoreflectance microscopy with submicrometer spatial resolution and up to 10 mK temperature resolution. Thin-film thermal conductivity is extracted by fitting a measured surface temperature distribution to a 3D finite element temperature model. The method is demonstrated by estimating thermal conductivity for an isotropic thin-film metal (nickel, 60–260 nm) on a glass substrate. The fitted Ni thermal conductivity was 50 ± 5 W/m K, which is in good agreement with the literature. Also, we present a detailed finite element analysis for an anisotropic thin-film semiconductor sample to show how the method could be extended to estimate thermal conductivity of anisotropic thin films. Advantages of the new method are easy sample preparation (no top surface transducer film or integrated heater required), rapid in situ measurement, and application to a broad range of thin-film materials. [ABSTRACT FROM AUTHOR]

Roll‐to‐Roll (R2R) manufacturing is changing how state‐of‐the‐art technology is made. Roll‐to‐Roll is part of a family of advanced scalable inline manufacturing techniques that make traditional and state‐of‐the‐art products at high yield and reduced cost. R2R manufacturing has grown rapidly and is fundamental to several advanced technologies such as functional materials and films, sensors for medicine, biology, and environment monitoring, energy harvesting devices, and flexible electronics. Advantages of R2R manufacturing include ease of machine design, adaptability to a wide range of additive processing methods, and very high throughput. To keep up with advances in R2R manufacturing, novel methods have emerged to measure important product metrics (thickness, roughness, conductivity) and monitor quality (uniformity, defects) inline and in real‐time. This review provides an overview of the state‐of‐the‐art for real‐time inline metrology and quality control in modern R2R manufacturing. The survey considers both established inline metrology techniques such as line‐scan imaging and reflectometry, and techniques recently adapted or that show promise for real‐time inline R2R metrology such as ellipsometry, hyper‐spectral imaging, and Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Electromigration (EM) is a phenomenon whereby the flow of current in metal wires moves the underlying atoms, potentially inducing electronic interconnect failures. The continued decrease in commercial lithographically defined feature sizes means that EM presents an increasing risk to the reliability of modern electronics. To mitigate these risks, it is important to look for novel mechanisms to extend lifetime without forfeiting miniaturization. Typically, only the overall increase in the interconnect resistance and failure voltage are characterized. However, if the current flows non-uniformly, spatially resolving the resulting hot spots during electromigration aging experiments may provide better insights into the fundamental mechanisms of this process. In this study, we focus on aluminum interconnects containing asymmetric reservoir and void pairs with contact pads on each end. Such reservoirs are potential candidates for self-healing. Thermoreflectance imaging was used to detect hot spots in electrical interconnects at risk of failure as the voltage was gradually increased. It reveals differential heating with increasing voltage for each polarity. We find that while current flow going from a constriction to a reservoir causes a break at the void, the identical structure with the opposite polarity can sustain higher current (J=21×106 A/cm2) and more localized joule heating and yet is more stable. Ultimately, a break takes place at the contact pad where the current flows from narrow interconnect to larger pads. In summary, thermoreflectance imaging with submicron spatial resolution provides valuable information about localized electromigration evolution and the potential role of reservoirs to create more robust interconnects. [ABSTRACT FROM AUTHOR]

The role of a HfO2 or ZrO2 interlayer as a thermal bridge between a $\beta $ -Ga2O3 channel and a sapphire substrate was investigated using a $\beta $ -Ga2O3 nano-membrane FET as a test vehicle. A 35% less channel temperature increase was observed when a thin HfO2 or ZrO2 interlayer was inserted between the $\beta $ -Ga2O3 channel and the sapphire substrate compared to devices without interlayers. Phonon density of states (PDOS) mismatch can explain the improvement of the thermal boundary conductance (TBC). In the acoustic region, the PDOS of HfO2 or ZrO2 has about a 700% larger overlap area with the PDOS of $\beta $ -Ga2O3 compared to the PDOS of sapphire. This suggests that the insertion of a thermal bridge interlayer can provide a potential solution to the low thermal conductivity of $\beta $ -Ga2O3 and the self-heating effect of $\beta $ -Ga2O3-based FETs. [ABSTRACT FROM AUTHOR]

In this work, we report back-end-of-line (BEOL) compatible indium-tin-oxide (ITO) transistors with ferroelectric (FE) Hf0.5Zr0.5O2 (HZO) as gate insulator. A tunable high-density 2-D electron gas over 0.8 × 1014/cm2 is achieved at the HZO/ITO oxide/oxide interface because of the FE polarization, which is confirmed by I – V, positive up and negative down (PUND), and Hall measurements. Such high carrier density can be completely modulated and switched on and off by FE polarization switching, enabling high mobility ITO transistor with high ON-current and high ON/OFF ratio. [ABSTRACT FROM AUTHOR]

Graphene-nanowire hybrid films have recently shown excellent performance as transparent conducting electrodes. However, due to their fundamental nonhomogeneity (grain boundaries, nanowire–nanowire junctions), self-heating induces hotspots along the co-percolating electrical conduction pathways. Although the steady-state characteristics of the hotspot temperature and location have been reported, the temporal response of the hotspots has not been studied in detail. In this paper, we use transient thermoreflectance imaging with high temporal resolution to quantify the transient characteristics of the hotspots. At local hotspots as well as nearby intermediate temperature regions, the temperature response in both heating and cooling phases exhibits two distinct time constants. We quantitatively determine the thermal time constants and associated amplitudes and show dependence of these parameters on distance from the contact. Based on solutions to heat diffusion equations, the short-time constant is attributed to the local self-heating within the hotspot region, and the long-time constant to diffusion of heat through the channel region. The knowledge of time evolution of hotspots and hence a more detailed understanding of the electrothermal conduction process through co-percolating networks could enable more reliable, advanced transparent conductors as well as one-dimensional/two-dimensional hybrid materials for other applications. [ABSTRACT FROM PUBLISHER]

We have demonstrated that depletion/enhancement-mode α-Ga2O3 on insulator field-effect transistors can achieve a record high drain current density of 1.5/1.0 A/mm by utilizing a highly doped α-Ga2O3 nano-membrane as the channel. α-Ga2O3 on insulator field-effect transistor (GOOI FET) shows a high on/off ratio of 1010 and low subthreshold slope of 150 mV/dec even with 300 nm thick SiO2. The enhancement-mode GOOI FET is achieved through surface depletion. An ultra-fast, high resolution thermo-reflectance imaging technique is applied to study the self-heating effect by directly measuring the local surface temperature. High drain current, low Rc, and wide bandgap make the α-Ga2O3 on insulator field-effect transistor a promising candidate for future power electronics applications. [ABSTRACT FROM AUTHOR]

Electroreflectance microscopy is demonstrated as a high-resolution, non-contact method to image dynamic charge distribution in integrated microsupercapacitor structures during fast voltage cycling. Electroreflectance camera images of a gold electrode H3PO4 polymer electrolyte microsupercapacitor reveal time varying charge distribution with submicron spatial resolution, millisecond time resolution, and electroreflectance resolution on the order of 500 nC cm−2. A model describing changes in the metal electrode's optical constants as a function of free electron concentration shows good agreement with measured electroreflectance. The proposed method can be used for sensitive, non-contact measurements of charge spatial distribution, and defect and performance characterization in electrode–electrolyte microdevices. [ABSTRACT FROM AUTHOR]