Matthias Schreiter

A 128 128 CMOS Biosensor Array for Extracellular Recording of Neural Activity

Sensor arrays are a key tool in the field of neuroscience for noninvasive recording of the activity of biological networks, such as dissociated neurons or neural tissue. A high-density sensor array complementary metal–oxide–semiconductor chip is presented with 16 K pixels, a frame rate of 2 kiloframes per second, and a pitch of 7.8 m 7.8 m for imaging of neural activity. The related circuit and system issues as well as process aspects are discussed. A mismatch-canceling calibration circuitry with current mode signal representation is used. Results from first biological experiments are presented, which prove full functionality of the chip.

A 128 /spl times/ 128 CMOS bio-sensor array for extracellular recording of neural activity

A CMOS sensor array for monitoring neural signals of living cells with 128 /spl times/ 128 pixels in a 1 mm/sup 2/ area is described. A standard 0.5 /spl mu/m, 5 V CMOS process extended by top electrodes covered by a relatively thin bio-compatible dielectric is used. Detection circuitry is based on a sensor-MOSFET mismatch-compensating current-mode technique.

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.

Optimized PZT Thin Films for Pyroelectric IR Detector Arrays

A planar multi target sputtering technology was used to deposit highly (111) oriented Pb(ZrxTi1−x)O3 (PZT) thin films with x ranging from 0–0.6. The preparation of a stable Pt/ZrO2 electrode is described and analyzed in terms of stress and stress-temperature behavior. The PZT films with low Zr content are under compressive stress after deposition. The dielectric constant and loss peaks occur at a composition close to the morphotropic phase boundary. Films on the tetragonal side of the phase diagram with a Zr content up to about 25% exhibited a strong self polarization and strong voltage shifts in the C(V) curves. High pyroelectric coefficients of >2×10−4 C/(m2K) have been measured on these films without additional poling. The self polarization fades out with increasing Zr content. The low values of the pyroelectric coefficient for the PZT film with 60% Zr is discussed in terms of the possible crystallographic variants after distortion and the tensile stress state during the phase transition. Based on the systematic study of stress and electrical properties of PZT films with a wide range of composition presented in this paper, films with a Zr content up to about 25% turned out to give the best properties for the use in pyroelectric detector arrays.

CMOS-Integrated Film Bulk Acoustic Resonators for Label-Free Biosensing

The throughput is an important parameter for label-free biosensors. Acoustic resonators like the quartz crystal microbalance have a low throughput because the number of sensors which can be used at the same time is limited. Here we present an array of 64 CMOS-integrated film bulk acoustic resonators. We compare the performance with surface plasmon resonance and the quartz crystal microbalance and demonstrate the performance of the sensor for multiplexed detection of DNA.

Sputtering of self-polarized PZT films for IR-detector arrays

Within a 3-year project a pyroelectric detector array based on a tetragonal Pb(Zr,Ti)O/sub 3/ (PZT) thin film on a silicon substrate was developed. Compositions of about 25-30% Zr showed best properties for the application in pyroelectric sensing systems. For the film deposition, planar multi target sputtering from 3 metallic targets in a reactive Ar/O/sub 2/ mixture is used. The advantage of this method is that the perovskite phase can be grown down to relatively low substrate temperatures of about 500/spl deg/C, a strong self polarization for compositions Zr/(Zr+Ti)<0.3 and a convenient control of the stoichiometry simply by varying the power supplied to the individual targets. The developed chip has (11/spl times/6) elements, his overall size is (8/spl times/4,7) mm/sup 2/. The array pixels of 280/spl times/280 /spl mu/m/sup 2/ have a noise equivalent power NEP of less than 0.7 nW at 1 Hz. The achieved specific detectivity D/sup */ at a modulation frequency of 10 Hz is 3/spl middot/10/sup 8/ cm/spl middot/Hz/sup 1/2//W.

A CMOS-based sensor array for in-vitro neural tissue interfacing with 4225 recording sites and 1024 stimulation sites

A CMOS-based microelectrode array (MEA) with 4225 recording sites and 1024 stimulation sites and a related data acquisition system are presented. The chip provides high spatiotemporal resolution on an active area of 1 mm × 1 mm or 2 mm × 2 mm, respectively, and allows in-vitro neural tissue interfacing experiments with full imaging capability. The entire chip surface is covered by a thin high-k dielectric layer so that electric coupling between biological tissue and solid-state chip is purely capacitive. Biological experiments reveal proper functionality of the system.