Robert Primig

First results on label-free detection of DNA and protein molecules using a novel integrated sensor technology based on gravimetric detection principles.

A novel integrated bio-sensor technology based on thin-film bulk acoustic wave resonators on silicon is presented and the feasibility of detecting DNA and protein molecules proofed. The detection principle of these sensors is label-free and relies on a resonance frequency shift caused by mass loading of an acoustic resonator, a principle very well known from quartz crystal micro balances. Integrated ZnO bulk acoustic wave resonators with resonance frequencies around 2 GHz have been fabricated, employing an acoustic mirror for isolation from the silicon substrate. DNA oligos have been thiol-coupled to the gold electrode by on-wafer dispensing. In a further step, samples have either been hybridised or alternatively a protein has been coupled to the receptor. The measurement results show the new bio-sensor being capable of both, detecting proteins as well as the DNA hybridisation without using a label. Due to the substantially higher oscillation frequency, these sensors already show much higher sensitivity and resolution comparable to quartz crystal micro balances. The potential for these sensors and sensors arrays as well as technological challenges will be discussed in detail.

Solidly mounted ZnO shear mode film bulk acoustic resonators for sensing applications in liquids

Solidly mounted film bulk acoustic resonators (FBAR) operating at 850 MHz in the shear vibration mode have been fabricated. C-axis inclined zinc oxide (ZnO) thin films realized by modified reactive magnetron sputtering were used. Coupling factors k/sup 2/ of 1.7% and Q-factors of 312 were determined in air. Q-factors of 192 were measured in water, making these devices attractive for sensing applications in liquids, e.g., biosensing.

Electro-acoustic hysteresis behaviour of PZT thin film bulk acoustic resonators

Abstract Thin film bulk acoustic resonators (FBARs) based on Pb(Zr x Ti (1− x ) )O 3 (PZT) with varying compositions, ranging from x =0.25 to 0.6, were fabricated to investigate hysteresis-like dependencies of the resonance frequency and electro-mechanical coupling constant on bias voltage. The resonators, formed by a simple sandwich structure consisting of bottom electrode, PZT thin film and top electrode, arranged on a planar acoustic mirror, were designed to give a resonance frequency of about 2 GHz. PZT thin films were deposited in a planar multi target sputtering system using three metallic targets in a reactive Ar/O 2 mixture. For low Zr-content, where PZT is grown in the tetragonal phase, the parallel resonance frequencies are strongly dependent on the applied electric field, while the series resonance frequency is practically unaffected. This behaviour is completely different for rhombohedral PZT at higher Zr-content. Here the series resonance frequency becomes strongly field dependent, which can be attributed to 109°/71° domain switching. As a potential application based on the observed strong field dependence of the acoustic properties, a bandwidth-tuneable or programmable RF filter based on PZT FBARs is proposed.

Novel integrated FBAR sensors: a universal technology platform for bio- and gas-detection

In this paper the feasibility of thin film bulk acoustic resonators (FBAR), for applications in bio- and gas-detection, is shown for the first time. Solidly mounted, ZnO FBARs with frequencies around 2 GHz have been fabricated on silicon substrates. The dependence of the FBAR mass sensitivity on the design of the layer stack has been investigated exhibiting an optimized sensitivity of 2.5 Hz cm/sup 2//pg. Using a common protein assay the capability of detecting bio-molecules has successfully been proved. Gas sensing has been demonstrated by coating the FBAR with a humidity absorbing polymer. A strong non-linear dependence of the humidity sensitivity on the thickness of the polymer coating has been found. When the polymer thickness is far less than the acoustic wavelength, a pure mass dependent response occurs, leading to a negative shift in resonance frequency. Moreover, as the polymer thickness becomes significant, acoustic influences affect the response and the shift becomes large and positive. A sensitivity to humidity of up to two orders of magnitude higher than that of comparably coated quartz crystal micro-balances has been observed.

Deposition of self-polarized PZT films by planar multi-target sputtering

Abstract A planar multi target sputtering approach was used to deposit self polarized PZT films on TiO2/Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays. By using elevated substrate temperatures of about 450°C “in situ” growth of tetragonal PZT could be achieved. The films exhibited pyroelectric currents without poling. The pyroelectric coefficient was 2×10−4 C/m2K, the dielectric constant was 300 and dielectric loss tan δ was 0.01. The self polarization disappears after heating the sample to 600°C. Stresses were studied in the thin film processing for the bottom electrode and the PZT film. The TiO2/Pt electrode is under high tensile stress of 900 MPa after preparation. PZT has a small compressive stress of -60 MPa, the whole TiO2/Pt/PZT stack has a tensile stress of +80 MPa. This low stress level together with the self polarization and the good electrical properties makes the films suitable for the use in pyroelectric detector arrays.

Facet growth in selective area epitaxy of Inp by MOMBE

Abstract InP facet growth near SiO 2 mask edges during metalorganic molecular beam epitaxy is studied for various V/III ratios on (100) substrates with 2° misorientation towards (110). While ideal vertical layer growth occurs at high V/III ratio even up to 2 μm growth thickness, oblique (111) planes are kinetically favoured near mask edges at lower V/III ratio. The V/III ratio is a key parameter since it determines the facets with the lowest kinetically limited growth rate at the border of the growing layer. Also the diffusion length of mobile adsorbed species, by which additional features near mask edges and corners are explained, decreases with V/III ratio. Besides interfacet diffusion driven by concentration gradients between facets of different growth rate, there is evidence also for anisotropic diffusion along [0–1] on (100) InP. We speculate that this is the origin of the fine surface ripples on InP surfaces observed on one side near the SiO 2 masks.

PZT thin films grown by multi-target sputtering: Analysis of thin film stress

Abstract A planar multi target sputtering approach was used to deposit Pb(Zr, Ti)O3 (PZT) films with different composition on Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays. Low stress ferroelectric capacitor stacks are needed in these devices, because the sensing elements are arranged on thin micromachined membranes. PZT films with a Zr content of 10 at% (10/90) and 48 at% (48/52) were analyzed in terms of thin film stress. PZT (10/90) films were found in a slight compressed state and PZT (48/52) under tensile stress after deposition. Stress temperature curves were used to evaluate the Curie temperature of the films. From the stress temperature curves the spontaneous distortion of the ferroelectric given by the lattice parameters can be extracted. The lower Curie temperature in combination with the smaller spontaneous distortion of the PZT (48/52) film is the reason for the difference in the stress state after deposition.

A 11×6 element pyroelectric detector array utilizing self-polarized pzt thin films grown by sputtering

Abstract A planar multi target sputtering approach was used to deposit PbTiO3 (PT) and Pb(Zr, Ti)O3 (PZT) films on TiO2/Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays. PZT films with a Zr content of 28 at% (PZ28T) exhibited the best pyroelectric coefficient of typically 2×10−4 Cm−2K−1. The PZ28T films have been used for fabricating a two dimensional 11×6 pixel pyroelectric detector array on Si wafers. The array pixels with a sensitive area of 280 ×280 μm2 have a noise lequivalent power NEP of less than 0.7 nW at 1 Hz. It is planned to use the detector array in systems for motion detection.

Sputtering of PZT thin films for surface micromachined IR-detector arrays

Abstract A planar, multi-target sputtering approach was used to deposit tetragonal Pb(Zr, Ti)O3(PZT) films with Zr/(Zr+Ti) = 0.25−0.3 on Pt bottom electrodes for the use in thin film pyroelectric IR detector arrays. Low stress ferroelectric capacitor stacks are needed in these devices, because the sensing elements are arranged on thin surface micromachined membranes. In-situ deposited films exhibited the best electrical properties. Typical values for the dielectric constant, the dielectric loss and the pyroelectric coefficient are 250, 2×10−4 C/(m2K), respectively. Very strong imprint effects have been found in these films. Even after a heat treatment above the Curie point a pyroelectric coefficient of > 2×10−4 C/(m2K) has been found. This is advantageous for possible high temperature processing steps after PZT deposition in pyroelectric detector device manufaction.

Investigation of the scaling rules determining the performance of film bulk acoustic resonators operating as mass sensors

Solidly mounted (SMR-type) thin film bulk acoustic resonators operating at 2.2, 4.1, and 8.0 GHz and with lateral extents from 30 to 500 mum were fabricated and their performance as mass sensors was evaluated theoretically as well as experimentally. It was found that increasing the frequency leads to a principally improved performance of these devices. Problems arising for the horizontal as well as the vertical dimension and structure are investigated