Bruno Morana

An all-in-one nanoreactor for high-resolution microscopy on nanomaterials at high pressures

We present a new MEMS nanoreactor fully integrated on a single die. It enables atomic-scale imaging of nanostructured materials under the high pressures and temperatures that are typical for many industrial applications (14 bar and 660 °C). The reactor can therefore be used to study the behavior of e.g. catalysts in a transmission electron microscope (TEM). It has a shallow channel (0.5 µm), which is made with surface micromachining techniques and contains pillars that prevent bulging. Integrated with the channel are very thin windows (15 nm) and a resistive heater. The reactor is very transparent, enabling the imaging of atomic lattice fringes with a spacing down to at least 0.15 nm.

Wafer-level assembly and sealing of a MEMS nanoreactor for in situ microscopy

This paper presents a new process for the fabrication of MEMS-based nanoreactors for in situ atomic-scale imaging of nanoparticles under relevant industrial conditions. The fabrication of the device is completed fully at wafer level in an ISO 5 clean room and it is based on silicon fusion bonding and thin film encapsulation for sealed lateral electrical feedthroughs. The fabrication process considerably improves the performances of previous nanoreactors. The wafer-level assembly allows faster preparation of devices, hydrocarbon contamination is no longer observed and the control of the channel height leads to a better flow reproducibility. The channel is shown to be sufficiently hermetic to work in the vacuum of a transmission electron microscope while a pressure of 100 kPa is maintained inside the nanoreactor. The transparency is demonstrated by the atomic scale imaging of YBCO nanoparticles, with a line spacing resolution of 0.19 nm.

A silicon carbide MEMS microhotplate for nanomaterial characterization in TEM

We report a SiC MEMS microhotplate designed for high temperature characterization of nanomaterials in transmission electron microscopes (TEMs). The microhotplate integrates, for the first time, a microheater of doped polycrystalline silicon carbide (poly-SiC) and electron-transparent windows of amorphous SiC (a-SiCx) on a freestanding membrane of undoped poly-SiC. Our work focuses on the development of the SiC layers by LPCVD, as well as on their combination in the fabrication process. The microhotplates were demonstrated to operate at temperatures well beyond 700°C.

Heat flux sensor for power loss measurements of switching devices

The measurement of the power dissipated by a semiconductor device is of great importance for assessing system performance and reliability and to evaluate the overall efficiency of a power electronics systems. Efficiency measurement can be difficult when the device is highly efficient and the power losses are extremely low. Measurement errors can be introduced due to high frequency components in the waveforms. We present a calorimetric method based on a micromachined dual-sensor heat-flux measurement device that allows the estimation of the power dissipated by a semiconductor device. The system use a thermoelectric heat pump to keep the switching device at room temperature in order to minimise the heat exchanged with the ambient and improve therefore the precision of the measurement.

Microfabrication of large-area circular high-stress silicon nitride membranes for optomechanical applications

In view of the integration of membrane resonators with more complex MEMS structures, we developed a general fabrication procedure for circular shape SiNx membranes using Deep Reactive Ion Etching (DRIE). Large area and high-stress SiNx membranes were fabricated and used as optomechanical resonators in a Michelson interferometer, where Q values up to 1.3 × 106 were measured at cryogenic temperatures, and in a Fabry-Perot cavity, where an optical finesse up to 50000 has been observed.

CNT bundles growth on microhotplates for direct measurement of their thermal properties

Vertically aligned Carbon Nanotubes (CNT) arrays were successfully grown on top of a freestanding microhotplate, to investigate the thermal dissipation properties of CNT bundles and their applicability as heat exchanger. Two CNT configurations are employed: a group of six bundles, each with a diameter of 20 μm, and a single CNT bundle with a diameter of 200 μm. In both configurations the bundles are 70 μm high. The microhotplate consists of a platinum thin film microheater integrated on a freestanding silicon nitride membrane. The microhotplate is used as heat source and as temperature sensor. Results show that at 300 °C, 20% and 31% of power can be saved with the circular six and single bundle configurations, respectively.

Heat flux-based sensor for the measurement of the power dissipated by switching devices

The precise measurement of the power dissipated by a semiconductor device operating in fast dynamic conditions is an important issue in power conversion circuits to evaluate their overall efficiency. Measurement errors can be introduced in particular by the probes or by instruments that are transparent to high dv/dt and di/dt rates. For this reason, the use of bulky and expensive set-ups is often required. We present a simple method based on a micromachined dual-sensor heat-flux measurement device, coupled to a readout circuit, that allows the estimation by calorimetry of the dissipated power. By means of a controlled Peltier heat pump, the switching device is held at room temperature in order to minimise the heat exchanged with the ambient and improve therefore the precision of the measurement. The sensor could be in principle integrated within the switching device case itself, to allow the lifelong monitoring of the produced heat.

LPCVD amorphous SiC x for freestanding electron transparent windows

MEMS electron-transparent membranes made of low-stress silicon nitride are widely employed in electron microscopy. However, this material has limited resistance to electron beams. We therefore developed a layer of LPCVD SiC. Our layer is amorphous, uniform, continuous, low-stress, and has extremely low etch-rates in common wet etchants. As free-standing electron transparent window, it demonstrates a resistance to electron beam damage 3 times higher than low-stress LPCVD silicon nitride. Our SiC layer could be advantageously employed in other MEMS devices, especially those operating in harsh environments, and in applications where high etching selectivity is required.

A mixing surface acoustic wave device for liquid sensing applications: Design, simulation, and analysis

This work presents the mixing wave generation of a novel surface acoustic wave (M-SAW) device for sensing in liquids. Two structures are investigated: One including two input and output interdigital transducer (IDT) layers and the other including two input and one output IDT layers. In both cases, a thin (1 μm) piezoelectric AlN layer is in between the two patterned IDT layers. These structures generate longitudinal and transverse acoustic waves with opposite phase which are separated by the film thickness. A 3-dimensional M-SAW device coupled to the finite element method is designed to study the mixing acoustic wave generation propagating through a delay line. The investigated configuration parameters include the number of finger pairs, the piezoelectric cut profile, the thickness of the piezoelectric substrate, and the operating frequency. The proposed structures are evaluated and compared with the conventional SAW structure with the single IDT layer patterned on the piezoelectric surface. The wave disp...

SAW device for liquid vaporization rate and remaining molecule sensing

This paper presents an Aluminum Nitride (AlN) surface acoustic wave (SAW) device for liquid detection, based on remaining liquid molecules and vaporization rate. The sensing mechanism of the SAW device uses linear attenuation and frequency shift during the vaporization process of the liquid. As the device is meant to operate with liquids, the piezoelectric film and metal interconnects are protected by a silicon oxide layer. A change in insertion loss is measured when liquid drops (0.5-2 μl) of demi-water (DW), isopropyl alcohol (IPA) and ethanol (ETH) are applied on the surface of the SAW device. The selected liquids have different equilibrium vapor pressures and boiling points. The vaporization process of DW is slow enough for the network analyzer to measure linear changes in the insertion loss parameter. For IPA and ETH, there is a frequency shift caused by the appearance of remaining molecules on the surface after they vaporize. The center frequency is shifted by 0.25 MHz for ETH and 0.198 MHz for IPA.