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
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  direction. Horizontal axis: a; vertical
axis, c. c) FMOF-3 viewed, in perspective, along the 
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.