Anna Górecka-Drzazga

Silicon optical pressure sensor

Abstract A novel optical-fiber silicon pressure sensor with a bossed membrane has been fabricated. The pressure deflects the micromachined thin membrane and moves the end of a fiber illuminating the p-n junction fabricated near the edge of the membrane in a standard IC process. A photovoltage proportional to the degree of deflection of the membrane is generated in the junction. A nontypical output voltage versus inlet pressure characteristic has been obtained.

Self-compensating piezoresistive pressure sensor

Abstract A double-bridge method of pressure-sensor compensation has been tested. Three types of sensors are produced: standard with a flat, square, thin membrane and single Wheatstone bridge with four diffused piezoresistors in standard configuration and new sensors with ‘cut’ piezoresistors and a flat or bossed square membrane with two identical Wheatstone bridges. One bridge is active, positioned on the membrane, sensitive to pressure and to all types of process- and temperature-induced errors. The other is inert, 100 μm away from the membrane and theoretically not sensitive to pressure. The good quality of new sensors with ‘cut’ piezoresistors has been confirmed. A good sensitivity of 250 mV (100 kPa, 5 V d.c.) has been obtained. Proper connection of the active and inert bridges has compensated the off-set voltage and temperature drift of the off-set voltage from values V off ,=110 mV to 40 mV and TCV off =0.15%/°C to 0.01-0.05%/°C. Tests of die and wafer-scale distributions show that statistical variations of V off may not be self-compensated by the use of the double-bridge method. The unexpectably high sensitivity of the inert bridge shows deep surface-stress penetration in the pressure-sensor die, which may destruct the stability of CMOS on-chip circuits. A modification of the double-bridge compensation method has been proposed.

Mold-type field-emission array fabrication by the use of fast silicon etching

The SiC sharp-emitter field-emission arrays have been produced by a transfer-mold technique. An alternate method of microwave-enhanced wet anisotropic silicon etching has been applied to the fabrication of field-emission arrays. Supporting, back side (100)-oriented, 380 μm thick silicon substrate has been etched away six times faster as compared to the thermally activated, standard KOH etching process. The alternate etching method may be successfully applied to any existing transfer-mold fabrication procedures.

Desorption/ionization mass spectrometry on array of silicon microtips

We have shown that a sample of bio-species deposited onto the spot of the array of protruded metal gated silicon tips (DIOST) may be effectively ionized and evaporated by UV laser pulsed light illumination. This phenomenon has been never observed on flat surface of silicon dioxide or TiW-Au thin film layers the materials which were used in construction of the tips array. Nature of this process is not known; the most intriguing fact is the protonization as well as negative electron ionization of bio-samples. The new DIOST platform was used for TOF MS tests, and clearly readable, low-noised mass spectrograms of LGG and dopamine were observed.

4-t-butyl-CuPc-PODT molecular composite material for an effective gas sensor

The sensing properties of molecular composites, tetratertbutyl copper phthalocyanine (TBCPC) and polyoctadecyl thiophene (PODT), were investigated by optical and conductance measurements. A standard substrate for gas sensing was made, consisting of a set of eight interdigitated gold electrodes, 230 /spl mu/m wide and spaced, and 0.10 /spl mu/m thick, photo-lithographically fixed on an SiO/sub 2/ coated silicon wafer. LB films of different thickness and composite compositions were fabricated at different surface pressures. The gas sensing behavior of the films, on exposure to NO/sub 2/ and NH/sub 3/ gases, depends on the mutual ratio of components of the composite. The film thickness determines the response speed on exposure to gases and their reversal. It was also found that the films deposited at lower surface pressures show larger and faster response and better recovery kinetics. The electrical properties of gold contacts to these Langmuir-Blodgett (LB) layers were evaluated by current-voltage characteristics, which are linear over the whole measuring range. Very short response times, reasonably good reproducibility, and fair composition dependent sensitivity at room temperature make this molecular composite a very promising candidate for neuron network sensing elements.

SiC field emitter arrays fabricated by transfer mold technique

The field emission arrays of SiC sharp emitter tips have been produced for the first time by use of the transfer mold technique. The test structures of active gun, containing approximately 3×104 of emitters, were prepared. The field emission current and work function calculations for SiC emitter arrays have been presented.

Micropump for Generation and Control of Vacuum Inside Miniature Devices

The microengineered MEMS-type ion-sorption micropump with field-emission electron source has been shown. Effective emission properties of the carbon nanotubes cathode ensure satisfactory efficiency of residual gas ionization, showing possibility of active pumping of circa 0.05 cm3 volume down to 10-5 hPa. Measurement of ion current allows estimation of vacuum level inside the microcavity.

Field-emission light sources utilizing carbon nanotubes and composite phosphor made of SiO2 nanospheres covered with Y2O3:Eu

A new concept of field-emission light sources (FELS) with electrophoretically deposited carbon nanotubes and newly discovered nanocomposite phosphor is presented. The vacuum micromachined devices were fabricated from silicon and glass wafers. Two types of miniature devices were tested. The first consisted of the silicon cathode covered with indium-tin oxide (ITO) layer and carbon nanotubes. The anode was made of glass wafer covered with ITO contact layer and nanocomposite core-shell phosphor. Nanocrystalline composite phosphor was made of silica core spheres covered with europium doped yttrium oxide Y2O3:Eu shell. For this model structure bright and uniform light emission was obtained. The second type of light source consisted of SiO2∕Y2O3:Eu phosphor deposited onto cathode, directly on carbon nanotubes layer. For this device successful but nonuniform luminescence was observed. Fabricated FELS are technologically compatible with microsystem technology and can be integrated with microfluidic systems.

A micromachined silicon-based probe for a scanning near-field optical microscope on-chip

The novel concept of an integrated scanning near-field optical microscope on-chip (SOMOC) has been presented. SOMOC consists of a micromachined cantilever probe and an emission-detection device realized by the use of a vertical-cavity surface-emitting laser (VCSEL). The construction and the first technological results of the silicon probe with a light transparent SiO2 tip have been described. The basic mechanical properties of the probe have been determined by stroboscopic interferometry.

Silicon components for gas chromatograph

A gas analyzer based on chromatography method using silicon- glass components has been built. Its main components were made by using MAMS-like technology, and its conception is concurrent to the idea of an integrated silicon chromatography proposed by SC Terry.