W. van der Vlist

A silicon-silicon nitride membrane fabrication process for smart thermal sensors

Abstract A new structure consisting of a silicon membrane suspended in a nitride membrane has been realized. This structure combines the advantages of the high thermal isolation of nitride membranes and the use of bipolar devices as sensing elements. The nitride membrane and the silicon membrane are fabricated within a single etch step. The process and its options are described by a design that includes several mono-Si thermopiles in a 2.5 μm thick silicon membrane and poly-Si thermopiles resting on a 0.3–0.8 μm thick oxide/nitride membrane. In all cases diodes, transistors and heating resistors are integrated as well. To prove the versatility of this process, as well as to,indicate which thermal configuration is more suitable for a specific application, a number of sensors realized with.this process will be briefly described.

Two-Dimensional Fiber Positioning and Clamping Device for Product-Internal Microassembly

In this paper, we present a microelectromechanical systems-based two-degrees-of-freedom positioning device combined with a clamping structure for positioning and constraining an optical fiber. The fiber position can be controlled in the two directions perpendicular to the fiber axis using two specifically designed wedges that can be accurately moved in-plane. These wedges are positioned using in-plane thermal actuators. Actuation of a fiber tip greater than 25 mum in-plane and 40 mum out-of-plane is achieved with a displacement resolution better than 0.1 m. After aligning the fiber the final position can be maintained by switching off the mechanical clamp, which also uses thermal actuators. The position of the fiber can be kept within 0.1 mum after switching off the mechanical clamp and the positioning actuator. Fiber-to-fiber alignment experiments have been performed and the technique can be extended to fiber-to-laser alignment.

Design and fabrication of infrared detector arrays for satellite attitude control

Abstract This paper describes the design, modelling and fabrication of infrared detectors for attitude control systems (ACS) for satellites. After a short introduction on the use and control of satellites in general, we explain the advantages of our integrated arrays of infrared detector units (pixels). Two types of detectors have been manufactured, a staggered array (ISA) with 32 pixels (in two staggered arrays of 16 pixels each) or in a cross of four staggered arrays (FPA) having 128 pixels in total. The choice depends upon the specific application (geostationairy or GEO orbit or low-altitude orbit). The detectors are based on a bipolar silicon process for the mechanical structure (electrochemically controlled etching (ECE)-KOH etching), with a SiN membrane for thermal isolation of the pixels, which have a polymer black coating for transduction of radiation to heat and n-type vs. p-type polysilicon thermopiles for heat detection. The pixel pitch is 600 μm, the black area is about 495×440 μm and the pixel sensitivity is about 55 V/W, at a thermopile resistance of 23.5 kΩ. The ISA measures in its present form 13.5×4 mm, the FPA measures 20.5×20.5 mm.

Thermogravimetric device with integrated thermal actuators

This paper presents the first MEMS device for ThermoGravimetric Analysis (TGA) with integrated thermal actuators. It consists of a sensing cantilever paddle connected to two separated thermal actuators, one at each side of the cantilever. Moreover, it has an integrated thermocouple that allows combined TGA and calorimetric measurements. To demonstrate the device performance TGA of copper sulfate pentahydrate (CuSO4·5H2O) samples has been performed. The operation range for the TGA device is 40 pg up to 0.1 µg for the mass and 25 up to 650 °C for the temperature. The mass sensitivity is about 200 Hz for a 1 ng sample on the 10 kHz resonance frequency.

MEMS hotplates with TiN as a heater material

Titanium nitride has been investigated as a heater material for hotplates and microreactors. TiN is CMOS compatible, and has a higher melting point (2950 degC) than conventional heaters of Pt and poly-Si. For the first time, TiN is tested inside a conventional membrane of LPCVD SiNx. Two types of TiN are considered: high stress and low stress. Their performance is compared with that of Pt. The maximum temperature of TiN coils is 11% higher than Pt coils with the same layout and over 700 degC. For high-stress TiN, the TCR is almost constant and close to that of Pt, making it very suitable for temperature sensing. In the case of low-stress TiN the TCR becomes nonlinear and changes sign. The large differences between the nitrides are explained by the grain structure. Low-stress TiN contains many voids. They relax stress but strongly scatter the conduction electrons. The different grain structures are related to the sputtering parameters according to the Thornton model

MEMS for Thermogravimetry: Fully Integrated Device for Inspection of Nanomasses

This paper presents a microelectromechanical-systems device for thermogravimetric analysis (TGA) with integrated thermal actuators. It consists of a sensing cantilever paddle connected to two separated thermal actuators, one at each side of the cantilever. An integrated thermocouple allows to measure directly the temperature difference between the heater at the tip of the cantilever paddle and the device silicon frame. The cantilever paddle vibration amplitude (frequency) is measured with an integrated piezoresistor. The temperature dependence of the resonance frequency on local heating with the integrated heater is investigated. Mass and temperature calibrations are performed from 0 to 6 ng and from 300 K to 823 K, respectively. To demonstrate the device performance, TGA of polyamide 6 and paraffin samples is carried out. TGA can be performed with the presented device in the temperature range from 298 K up to 920 K for sample masses as small as 0.8 ng. The mass sensitivity is about 164 Hz/ng at ambient temperature.

Aluminum passivation in saturated TMAHW solutions for IC-compatible microstructures and device isolation

Tetramethyl ammonium hydroxide (TMAH) solutions have been used to realize IC-compatible micromachined structures and device isolation. THe very low etch rate of PECVD dielectric layers and the possibility to passivate the aluminum metalization by doping the solution with silicon, increase the range of applications of this etchant and simplify both the post processing and the etch set-up configuration. Solutions of TMAH and water with addition of solid silicon or silicic acid have been used to study the effect of solution saturation on the passivation of aluminum. The etch rate of silicon, selectivity to masking materials and quality of the etched surfaces has been evaluated in both types of doped solutions in the temperature range 70 degrees-90 degrees C. An etch rate of less than 10nm/hr for the Al/1 percent Si metal layer has been measured in the saturated solutions. Further, the use of additives, such as IPA and pyrocatechol, on the etchant characteristics has been investigated. The addition of IPA has little or no influence on the etching characteristics, while very little quantities of pyrocatechol are sufficient to cause major improvements on the etching uniformity and surface quality, with no negative effect on the aluminum passivation.

A novel silicon interposer for measuring devices requiring complex two-sided contacting

The design and fabrication process is presented for a novel silicon-based interposer suitable for dies where it is necessary to place multiple contact pads on the both sides of wafer. This interposer transfers all contacts to the same side of the wafer so that the measurement can be done using conventional probe stations for one-sided probing.

Self-cleaning mass calibration of a thermogravimetric device using a thin-film molybdenum

This paper presents a self-cleaning mass calibration procedure for a thermogravimetric (TC) device using molybdenum (Mo). A Mo thin-film is deposited by sputtering and patterned with known geometry on the device sample area using a standard lithography step thus giving accurate control of the mass of the sample under investigation. The device resonance frequency is measured while the temperature of the sample area is increased from room temperature to about 923 K using the integrated heater. First the Mo oxidizes. Then, at temperatures above 773 K the Mo trioxide (MoO3) evaporates. This causes a shift in resonance frequency that can be linked to the known initial mass of the Mo. An advantage of this method is that, the Mo leaves the device clean and ready for TG analysis (TGA) of other samples.

Fabrication of nanochannels using glass to glass anodic bonding

In this work, we present a technology for fabrication of nanochannels created in glass with which bio-analysis can be performed in combination with fluorescence microscopy. The technology is based on a glass-to-glass anodic bonding process. In the bonding process, an intermediate layer (thin insulating film) is deposited on one of the two glass wafers. The channel is then defined, with one photo-patterning step, in the intermediate layer. In our approach, a 33 nm thick amorphous silicon layer (deposited by LPCVD) was used as an intermediate layer. The depth of the channel is defined during the etching of this layer.