Next-Gen electronics: Chemical vapour deposition of zeolitic imidazolate framework thin films

Next-Gen electronics: Chemical vapour deposition of zeolitic imidazolate framework thin films

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Next-Gen electronics: Chemical vapour deposition of zeolitic imidazolate framework thin films
Next-Gen electronics: Chemical vapour deposition of zeolitic imidazolate framework thin films

Integrating metal–organic frameworks (MOFs) in microelectronics has disruptive potential because of the unique properties of these microporous crystalline materials. Suitable film deposition methods are crucial to leverage MOFs in this field. Conventional solvent-based procedures, typically adapted from powder preparation routes, are incompatible with nanofabrication because of corrosion and contamination risks.

The procedure consists of a metal oxide vapour deposition (Step 1) and a consecutive vapour–solid reaction (Step 2). Metal, oxygen and ligand sources are labelled as M, O and L, respectively. Metal oxide deposition can be achieved by atomic layer deposition (M, diethylzinc; O, oxygen/water) or by reactive sputtering (M, zinc; O, oxygen plasma). Atom colours: zinc (grey) oxygen (red), nitrogen (light blue) and carbon (dark blue); hydrogen atoms are omitted for clarity.
The procedure consists of a metal oxide vapour deposition (Step 1) and a consecutive vapour–solid reaction (Step 2). Metal, oxygen and ligand sources are labelled as M, O and L, respectively. Metal oxide deposition can be achieved by atomic layer deposition (M, diethylzinc; O, oxygen/water) or by reactive sputtering (M, zinc; O, oxygen plasma). Atom colours: zinc (grey) oxygen (red), nitrogen (light blue) and carbon (dark blue); hydrogen atoms are omitted for clarity.

A chemical vapour deposition process (MOF-CVD) that enables high-quality films of ZIF-8, a prototypical MOF material, with a uniform and controlled thickness, even on high-aspect-ratio features.

a, X-ray diffraction pattern of a ZIF-8 CVD film and simulated pattern for ZIF-8. b, Scanning electron microscopy top view. c, 3D rendered AFM topograph. d, Focused-ion beam TEM cross section. Inset: high-resolution magnification of the interface between ZIF-8 and the titanium oxide substrate. e, HAADF and EDS cross-section maps of a completely transformed film. f, HAADF and EDS cross-section maps of a partially transformed film. The completely transformed film (a–e) was obtained by vapour–solid reaction of a 6-nm-thick ALD zinc oxide film. The partially transformed film (f) was obtained by vapour–solid reaction of a 15-nm-thick ALD zinc oxide film. Scale bars, 2 μm for b–d, 20 nm for inset in d, 100 nm for e–f.
a, X-ray diffraction pattern of a ZIF-8 CVD film and simulated pattern for ZIF-8. b, Scanning electron microscopy top view. c, 3D rendered AFM topograph. d, Focused-ion beam TEM cross section. Inset: high-resolution magnification of the interface between ZIF-8 and the titanium oxide substrate. e, HAADF and EDS cross-section maps of a completely transformed film. f, HAADF and EDS cross-section maps of a partially transformed film. The completely transformed film (a–e) was obtained by vapour–solid reaction of a 6-nm-thick ALD zinc oxide film. The partially transformed film (f) was obtained by vapour–solid reaction of a 15-nm-thick ALD zinc oxide film. Scale bars, 2 μm for b–d, 20 nm for inset in d, 100 nm for e–f.

Furthermore, we demonstrate how MOF-CVD enables previously inaccessible routes such as lift-off patterning and depositing MOF films on fragile features.

a,b, Scanning electron microscopy images showing the ZIF-8-coated silicon pillar array. c,d, High-magnification scanning electron microscopy images showing the homogeneous coverage at the base of the pillars. e, Kr adsorption isotherms for the zinc-oxide-coated pillar array (grey circles) and after 15 min (red crosses), 30 min (blue diamonds) and 45 min (yellow squares) vapour–solid reaction. f, Single-pulse Kr adsorption kinetics experiment for a 85-nm-thick high-aspect-ratio ZIF-8 film (green) and a 2,500-nm-thick flat film (dashed, grey). Scale bars, 50 μm for a, 5 μm for b,c and 1 μm for d.
a,b, Scanning electron microscopy images showing the ZIF-8-coated silicon pillar array. c,d, High-magnification scanning electron microscopy images showing the homogeneous coverage at the base of the pillars. e, Kr adsorption isotherms for the zinc-oxide-coated pillar array (grey circles) and after 15 min (red crosses), 30 min (blue diamonds) and 45 min (yellow squares) vapour–solid reaction. f, Single-pulse Kr adsorption kinetics experiment for a 85-nm-thick high-aspect-ratio ZIF-8 film (green) and a 2,500-nm-thick flat film (dashed, grey). Scale bars, 50 μm for a, 5 μm for b,c and 1 μm for d.

The compatibility of MOF-CVD with existing infrastructure, both in research and production facilities, will greatly facilitate MOF integration in microelectronics.

a, Schematic overview of the transformation mechanism. b, Plot of the time-resolved diffraction patterns viewed down the intensity axis, showing the transformation of crystalline phases in a 1:2 mixture of crystalline zinc oxide and HmIM powder at 130 °C. Colour scale from blue (low intensity) to red (high intensity). Simulated pure-phase diffraction patterns are plotted at the top for reference and peaks corresponding to ZIF-8 are highlighted by the blue arrows. c, ZIF-8 phase quantification for in situ reaction experiments at 115 °C (blue) and 130 °C (red). d, ZIF-8 phase quantification for in situ reaction experiments at 115 °C under a continuous dry nitrogen flow (purple) and a nitrogen flow humidified to 33% relative humidity at room temperature (green).
a, Schematic overview of the transformation mechanism. b, Plot of the time-resolved diffraction patterns viewed down the intensity axis, showing the transformation of crystalline phases in a 1:2 mixture of crystalline zinc oxide and HmIM powder at 130 °C. Colour scale from blue (low intensity) to red (high intensity). Simulated pure-phase diffraction patterns are plotted at the top for reference and peaks corresponding to ZIF-8 are highlighted by the blue arrows. c, ZIF-8 phase quantification for in situ reaction experiments at 115 °C (blue) and 130 °C (red). d, ZIF-8 phase quantification for in situ reaction experiments at 115 °C under a continuous dry nitrogen flow (purple) and a nitrogen flow humidified to 33% relative humidity at room temperature (green).
a, Schematic diagram of MOF pattern deposition by MOF-CVD and subsequent lift-off of a patterned photoresist. b,c, Scanning electron microscopy images of the manufactured ZIF-8 patterns. d, Schematic diagram of the production of ZIF-8-coated polydimethylsiloxane pillars by soft lithography and MOF-CVD. e, Scanning electron microscopy image of MOF-CVD-coated PDMS pillars. f, Scanning electron microscopy image of identical PDMS pillars after conventional solution processing of ZIF-8. The MOF-CVD processing steps are indicated with a dashed line in a and d. Oxide and MOF films are represented in red and blue, respectively. Scale bars, 100 μm for b, 10 μm for c, 20 μm for e,f, 1 μm for insets.
a, Schematic diagram of MOF pattern deposition by MOF-CVD and subsequent lift-off of a patterned photoresist. b,c, Scanning electron microscopy images of the manufactured ZIF-8 patterns. d, Schematic diagram of the production of ZIF-8-coated polydimethylsiloxane pillars by soft lithography and MOF-CVD. e, Scanning electron microscopy image of MOF-CVD-coated PDMS pillars. f, Scanning electron microscopy image of identical PDMS pillars after conventional solution processing of ZIF-8. The MOF-CVD processing steps are indicated with a dashed line in a and d. Oxide and MOF films are represented in red and blue, respectively. Scale bars, 100 μm for b, 10 μm for c, 20 μm for e,f, 1 μm for insets.

MOF-CVD is the first vapour-phase deposition method for any type of microporous crystalline network solid and marks a milestone in processing such materials.

Nature Materials

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