OPERANDO INVESTIGATION OF FLUOROUS METAL ORGANIC FRAMEWORKS AND NON-POROUS COORDINATION POLYMERS AS ULTRALOW-κ MATERIALS
Fluorous metal organic frameworks (FMOFs) and fluorous non-porous coordination polymers (FN-PCPs) are promising alternatives to current low-κ dielectrics. The results of high-resolution operando powder X-ray diffraction (PXRD) studies on FMOF-3 and FN-PCP-1 concurred to shed light on their dielectric properties, enlightening their structural response under an alternate current.
STRUCTURE OF MATERIALS
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Due to an increased demand for transistors of decreased size and higher speed, integrated circuits (ICs) have been progressively modified [1-3]: presently, IC size is about tens of nanometres, which allows a microprocessor working frequency in the order of THz. Associated with this rising operational speed are signal propagation delay at the conductor-insulator interconnects, dynamic power consumption and electronic cross talk , which limit the overall performance of the device. To overcome these limits, dielectrics with a dielectric constant (κ) lower than that of silica (κ = 3.9-4.5) must be employed in the construction of ICs.
Recent theoretical and experimental investigations have revealed that fluorous metal organic frameworks (FMOFs) and non- porous coordination polymers (FN-PCPs) could be promising alternatives to current low-κ dielectrics as they potentially possess a number of desirable traits in one material such as: i) controlled and reproducible chemical composition and crystal structure that allow controlled and reproducible physico-chemical properties which is not always the case with amorphous materials and ii) low adsorptivity of high-κ species (water has κ ~ 80).
Within this landscape, the fluorinated ligand 1,4-bis(1-H-tetrazol-5-yl)tetrafluorobenzene (H2FBTB, Figure 138a) was synthesised and employed to build up the [Cu(FBTB) (DMF)] (DMF = N,N-dimethylformamide) and [Ag2(FBTB)] compounds (FMOF-3 and FN-PCP-1, respectively). In view of its metal centre (copper vs. silver), FMOF-3 represents a more economical alternative, whereas FN-PCP-1 provides a comparison term upon changing the metal ion but not the ligand.
Powder X-ray diffraction disclosed a 3D porous and non-porous polymeric architecture for FMOF- 3 and FN-PCP-1, respectively (Figures 138b-c). They possess experimental contact angles of ca. 86 and 75°. FN-PCP-1 is stable if exposed to water vapour for at least 48 days. Under ambient temperature and pressure, pellets of FMOF-3 and FN-PCP-1 exhibit κ values of 2.44(3) and 2.57(3), respectively, at 2×106 Hz. Such low-κ values are maintained even after pellet exposure to an almost saturated humidity environment.
High-resolution operando PXRD experiments (CH-4795) were performed at beamline ID22 on pellets of FMOF-3 and FN-PCP-1 in the absence of electric current and while applying an
Fig. 138: a) The molecular structure of
1,4-bis(1-H-tetrazol-5-yl) tetrafluorobenzene (H2FBTB). Representation of the crystal
structure of (b) FN-PCP-1 viewed, in perspective,
along the [010] direction. Horizontal axis: a; vertical
axis, c. c) FMOF-3 viewed, in perspective, along the [100]
direction. Horizontal axis, b; vertical axis, c. Element colour code: carbon, grey;
copper, fuchsia; fluorine, light green; nitrogen, blue; silver,
fuchsia. The clathrated solvent molecules in FMOF-3 have
been omitted for clarity.