Christophe Py

Room temperature deposition of ITO using r.f. magnetron sputtering

Using r.f. magnetron sputtering, indium tin oxide (ITO) films were deposited at room temperature on glass substrates. The effects of sputtering power and oxygen flow rate were examined and related to the physical properties of the films such as sheet resistance, optical transparency stress, crystallinity, and porosity. We demonstrate the deposition of ITO films at room temperature with a transparency between 70 and 90% in the visible spectrum and an 18 Ω/□ sheet resistance.

Design of high-contrast OLEDs with microcavity effect

There is a large demand for Organic Light-Emitting Displays (OLEDs) with higher contrast, particularly for outdoor applications. We show that lowering the reflectance of OLEDs, which is required for increasing the contrast, can also lead to a reduction of their efficiency when a small microcavity effect is not maintained in their structure. We describe in details the design of high-contrast bottom-emitting OLEDs that have low reflectance but still maintain a small cavity effect for efficient emission.

Microcavity organic light emitting diodes with double sided light emission of different colors

An organic light emitting diode was fabricated using a thin semitransparent Mg:Ag metal film (30 nm) and a distributed Bragg reflector with a reflectance of 99.5% as a microcavity. Double-sided electroluminescence was observed: green from the metal side and red from the glass side, both in directions normal to the surface. A maximum luminance of 2523 cd/m2 was obtained from the metal side, where most light was coupled out of the cavity.

Beam focusing characteristics of silicon microtips with an in-plane lens

Single microtips, 2/spl times/2 and 10/spl times/10 arrays of microtips surrounded by an integrated focusing ring, were fabricated and their focusing characteristics experimentally investigated. Observation of the beam on a phosphor screen shows that the focusing is very effective for single microtips and 2/spl times/2 arrays; moreover, the reduction in emitted current is much smaller than for double-gate focusing. 10/spl times/10 arrays of microtips, however, do not generate very focused beams. These results agree well with simulations. The possibility of simultaneous focusing and deflecting is also discussed, and a new structure combining the advantages of double-gate and surrounding ring focusing is suggested.

An integrated shadow-mask based on a stack of inorganic insulators for high-resolution OLEDs using evaporated or spun-on materials

Abstract While organic materials show impressive performances as electroluminescent diodes, their integration in a passive matrix to form a high-resolution display is a challenge. The anode can easily be patterned in columns prior to the deposition of organic materials, but conventional microfabrication techniques cannot be used to etch the cathode on top because organics are affected by treatments applied to photosensitive resins. We microfabricated an integrated shadow-mask with openings in rows orthogonal to the columns of the anode. The mask has an overhanging edge so that the cathode evaporated on top is discontinuous at its edges, thereby separating the diodes along rows. The mask is composed of a stack of inorganic insulators all deposited in a commercial plasma-enhanced chemical vapor deposition tool, and whose different etching rates in hydrofluoridric acid enable to obtain the overhang in one lithographic step. The process is very simple, as high resolution as microfabrication can provide, and the resulting device is less prone to short-circuits than when a lift-off photoresist is used. Pixellation is reported both from evaporated small molecules and spun-on polymers.

From Understanding Cellular Function to Novel Drug Discovery: The Role of Planar Patch-Clamp Array Chip Technology

All excitable cell functions rely upon ion channels that are embedded in their plasma membrane. Perturbations of ion channel structure or function result in pathologies ranging from cardiac dysfunction to neurodegenerative disorders. Consequently, to understand the functions of excitable cells and to remedy their pathophysiology, it is important to understand the ion channel functions under various experimental conditions – including exposure to novel drug targets. Glass pipette patch-clamp is the state of the art technique to monitor the intrinsic and synaptic properties of neurons. However, this technique is labor intensive and has low data throughput. Planar patch-clamp chips, integrated into automated systems, offer high throughputs but are limited to isolated cells from suspensions, thus limiting their use in modeling physiological function. These chips are therefore not most suitable for studies involving neuronal communication. Multielectrode arrays (MEAs), in contrast, have the ability to monitor network activity by measuring local field potentials from multiple extracellular sites, but specific ion channel activity is challenging to extract from these multiplexed signals. Here we describe a novel planar patch-clamp chip technology that enables the simultaneous high-resolution electrophysiological interrogation of individual neurons at multiple sites in synaptically connected neuronal networks, thereby combining the advantages of MEA and patch-clamp techniques. Each neuron can be probed through an aperture that connects to a dedicated subterranean microfluidic channel. Neurons growing in networks are aligned to the apertures by physisorbed or chemisorbed chemical cues. In this review, we describe the design and fabrication process of these chips, approaches to chemical patterning for cell placement, and present physiological data from cultured neuronal cells.

A novel silicon patch‐clamp chip permits high‐fidelity recording of ion channel activity from functionally defined neurons

We report on a simple and high‐yield manufacturing process for silicon planar patch‐clamp chips, which allow low capacitance and series resistance from individually identified cultured neurons. Apertures are etched in a high‐quality silicon nitride film on a silicon wafer; wells are opened on the backside of the wafer by wet etching and passivated by a thick deposited silicon dioxide film to reduce the capacitance of the chip and to facilitate the formation of a high‐impedance cell to aperture seal. The chip surface is suitable for culture of neurons over a small orifice in the substrate with minimal leak current. Collectively, these features enable high‐fidelity electrophysiological recording of transmembrane currents resulting from ion channel activity in cultured neurons. Using cultured Lymnaea neurons we demonstrate whole‐cell current recordings obtained from a voltage‐clamp stimulation protocol, and in current‐clamp mode we report action potentials stimulated by membrane depolarization steps. Despite the relatively large size of these neurons, good temporal and spatial control of cell membrane voltage was evident. To our knowledge this is the first report of recording of ion channel activity and action potentials from neurons cultured directly on a planar patch‐clamp chip. This interrogation platform has enormous potential as a novel tool to readily provide high‐information content during pharmaceutical assays to investigate in vitro models of disease, as well as neuronal physiology and synaptic plasticity. Biotechnol. Bioeng. 2010;107:593–600.

Organic light emitting diodes based on end-substituted oligo(phenylenevinylene)s

Abstract We report our investigation of the electroluminescent properties of multilayer organic light emitting devices using a series of three-phenyl-ring oligo(phenylenevinylene)s with poly(alkyleneoxy) electron-donors and hexylsulfonyl electron-acceptors as emitting materials. The emission color varies from blue to green depending on the substituted end-groups in the molecules. The insertion of hole blocking and electron injecting layers significantly improves the electroluminescent efficiency and extends the operational life time. The maximum electroluminescence efficiency reached is 1.9 cd/A for the blue diodes, and 2.3 cd/A for the blue-green diodes.

Cell placement and guidance on substrates for neurochip interfaces.

Interface devices such as integrated planar patch‐clamp chips are being developed to study the electrophysiological activity of neuronal networks grown in vitro. The utility of such devices will be dependent upon the ability to align neurons with interface features on the chip by controlling neuronal placement and by guiding cell connectivity. In this paper, we present a strategy to accomplish this goal. Patterned chemical modification of SiN surfaces with poly‐d‐lysine transferred from PDMS stamps was used to promote adhesion and guidance of cryo‐preserved primary rat cortical neurons. We demonstrate that these neurons can be positioned and grown over microhole features which will ultimately serve as patch‐clamp interfaces on the chip. Biotechnol. Bioeng. 2010; 105: 368–373.

High-fidelity patch-clamp recordings from neurons cultured on a polymer microchip

We present a polymer microchip capable of monitoring neuronal activity with a fidelity never before obtained on a planar patch-clamp device. Cardio-respiratory neurons Left Pedal Dorsal 1 (LPeD1) from mollusc Lymnaea were cultured on the microchip’s polyimide surface for 2 to 4 hours. Cultured neurons formed high resistance seals (gigaseals) between the cell membrane and the surface surrounding apertures etched in the polyimide. Gigaseal formation was observed without applying external force, such as suction, on neurons. The formation of gigaseals, as well as the low access resistance and shunt capacitance values of the polymer microchip resulted in high-fidelity recordings. On-chip culture of neurons permitted, for the first time on a polymeric patch-clamp device, the recording of high fidelity physiological action potentials. Microfabrication of the hybrid poly(dimethylsiloxane)—polyimide (PDMS-PI) microchip is discussed, including a two-layer PDMS processing technique resulting in minimized shrinking variations.