Qun Jin

Multidimensional integration and multifunctional component assembly have been greatly explored in recent years to extend Moore’s Law of modern microelectronics. However, this inevitably exacerbates the inhomogeneity of temperature distribution in microsystems, making precise temperature control for electronic components extremely challenging. Herein, we report an on-chip micro temperature controller including a pair of thermoelectric legs with a total area of 50 × 50 μm², which are fabricated from dense and flat freestanding Bi₂Te₃-based thermoelectric nano films deposited on a newly developed nano graphene oxide membrane substrate. Its tunable equivalent thermal resistance is controlled by electrical currents to achieve energy-efficient temperature control for low-power electronics. A large cooling temperature difference of 44.5 K at 380 K is achieved with a power consumption of only 445 μW, resulting in an ultrahigh temperature control capability over 100 K mW⁻¹. Moreover, an ultra-fast cooling rate exceeding 2000 K s⁻¹ and excellent reliability of up to 1 million cycles are observed. Our proposed on-chip temperature controller is expected to enable further miniaturization and multifunctional integration on a single chip for microelectronics.

Flexible thermoelectric materials have attracted increasing interest because of their potential use in thermal energy harvesting and high‐spatial‐resolution thermal management. However, a high‐performance flexible micro‐thermoelectric device (TED) compatible with the microelectronics fabrication process has not yet been developed. Here a universal epitaxial growth strategy is reported guided by 1D van der Waals‐coupling, to fabricate freestanding and flexible hybrids comprised of single‐wall carbon nanotubes and ordered (Bi,Sb)₂Te₃ nanocrystals. High power factors ranging from ≈1680 to ≈1020 µW m⁻¹ K⁻² in the temperature range of 300–480 K, combined with a low thermal conductivity yield a high average figure of merit of ≈0.81. The fabricated flexible micro‐TED module consisting of two p–n couples of freestanding thermoelectric hybrids has an unprecedented open circuit voltage of ≈22.7 mV and a power density of ≈0.36 W cm⁻² under ≈30 K temperature difference, and a net cooling temperature of ≈22.4 K and a heat absorption density of ≈92.5 W cm⁻².

Flexible thermoelectric (TE) materials have attracted increasing interest due to their potential applications in energy harvesting and high-spatial-resolution thermal management. However, a high-performance flexible micro-TE device (TED) compatible with the modern electronics fabrication process has not yet been developed. Here we report a general van der Waals epitaxial growth approach to fabricating a freestanding and flexible hybrid comprised of single-wall carbon nanotubes and highly ordered (Bi,Sb)2Te3 nanocrystals. High power factors ranging from ~1,680 to ~1,020 µW m−1 K−2 in the temperature range of 300-480 K, combined with a strongly depressed thermal conductivity yield an average figure of merit of ~0.81. A prototype flexible micro-TED module consisting of two p-n hybrids was then fabricated, which demonstrated an unprecedented open circuit voltage of ~22.7 mV and a power density of ~0.36 W cm−2 under a ~30 K temperature difference, and a net cooling temperature of ~22.4 K and a heat absorption density of ~92.5 W cm−2.

Thin film thermoelectrics (TEs) with unique advantages have triggered great interest in thermal management and energy harvesting technology for ambient temperature microscale system. Although they have exhibited a good prospect, the unsatisfactory performances still seriously hamper their widespread application. Tailoring porous structure has been demonstrated to be a facile strategy to significantly reduce thermal conductivity and enhance the figure of merit (ZT) of bulk TE materials, however, which is yet challenging for thin film TEs. Here, the nanoporous Bi2Te3 thin films with faceted pore shape and various porosity, pore size and pore interval are carefully designed and fabricated by evacuating over-stoichiometry Te. The dependence of the carrier mobility and lattice thermal conductivity on the pore characters are deliberately investigated. In the case of the pore interval longer than the electron mean free path, the porous structure greatly reduces the lattice thermal conductivity without affecting the electrical conductivity obviously. Phonon specular backscattering that highly related to the pore characters is suggested to be mainly responsible for the thermal conductivity reduction, resulting in ~60% enhancement in ZT at room temperature, i.e. from ~0.42 for the dense film to ~0.67 for the nanoporous film. The enhanced ZT value is comparable to that of commercial bulk TEs and can be further improved by optimizing the carrier concentrations. This work provides a general approach to fabricate high-performance chalcogenide TE thin film materials.

Single-wall carbon nanotubes (SWCNTs) are ideal for fabricating transparent conductive films because of their small diameter, good optical and electrical properties, and excellent flexibility. However, a high intertube Schottky junction resistance, together with the existence of aggregated bundles of SWCNTs, leads to a degraded optoelectronic performance of the films. We report a network of isolated SWCNTs prepared by an injection floating catalyst chemical vapor deposition method, in which crossed SWCNTs are welded together by graphitic carbon. Pristine SWCNT films show a record low sheet resistance of 41 ohm □⁻¹ at 90% transmittance for 550-nm light. After HNO₃ treatment, the sheet resistance further decreases to 25 ohm □⁻¹. Organic light-emitting diodes using this SWCNT film as anodes demonstrate a low turn-on voltage of 2.5 V, a high current efficiency of 75 cd A⁻¹, and excellent flexibility. Investigation of isolated SWCNT-based field-effect transistors shows that the carbon-welded joints convert the Schottky contacts between metallic and semiconducting SWCNTs into near-ohmic ones, which significantly improves the conductivity of the transparent SWCNT network. Our work provides a new avenue of assembling individual SWCNTs into macroscopic thin films, which demonstrate great potential for use as transparent electrodes in various flexible electronics.

Porous modification is a general approach to endowing the rigid inorganic thermoelectric (TE) materials with considerable flexibility, however, by which the TE performances are severely sacrificed. Thus, there remains ongoing struggle against the trade-off between TE properties and flexibility. Herein, we develop a novel strategy to combine Bi2Te3 thick film with ubiquitous cellulose fibers (CFs) via unbalanced magnetron sputtering technique. Owing to the nano-micro hierarchical porous structures and the excellent resistance to crack propagation of the Bi2Te3/CF architectures, the obtained sample with nominal Bi2Te3 deposition thickness of tens of micrometers exhibit excellent mechanically reliable flexibility, of which the bending deformation radius could be as small as a few millimeters. Furthermore, the Bi2Te3/CF with rational internal resistance, tailorable shapes and dimensions are successfully fabricated for practical use in TE devices. Enhanced Seebeck coefficients are observed in the Bi2Te3/CF as compared to the dense Bi2Te3 films and the lattice thermal conductivity is remarkably reduced due to the strong phonon scattering effect. As a result, the TE figure of merit, ZT, is achieved as high as ~0.38 at 473 K, which competes the best flexible TEs and can be further improved by optimizing the carrier concentrations. We believe this developed technique not only opens up a new window to engineer flexible TE materials for practical applications, but also promotes the robust development of the fields, such as paper-based flexible electronics and thin-film electronics.