Norbert Neumann

Pyroelectric thin film sensors and arrays based on P(VDF/TrFE)

Abstract After a short description of the structure and operation of a pyroelectric sensor, the thermal conditions of the sensing element, the thermal-to-electrical conversion and the signal processing of pyroelectric thin film sensors will be represented. By means of the complex normalised current responsivity TR(jω, s) and figures of merit Mv, M1 and MD, an universal description of the sensors internal operation is obtained. The influence of electrothermal coupling effects on the dielectric loss of the pyroelectric thin film is also discussed. Substantial requirements to the pyroelectric thin film and the sensor design are derived. A comparison of often used thin film ferroelectrics shows that the application of P(VDF/TrFE) in low cost sensors can be advantageous although the figures of merit are lower. Copolymer film can be easily deposited onto a silicon wafer in post-processing after read out circuit fabrication, for instance by spin coating of a copolymer solution. Furthermore, the very low thermal...

Pyroelectric single-element and linear-array sensors based on P(VDF/TrFE) thin films

Abstract The application of pyroelectric poly(vinylidene fluoride/trifluoroethylene) (P(VDF/TrFE)) copolymer thin films simplifies the manufacture of pyroelectric single-element sensors and, above all, of sensor arrays with high sensitivity, low noise and slight crosstalk. The sensor consists of a self-supporting membrane that is a combination of silicon oxide and silicon nitride. This membrane is made by anisotropic etching on the back of a (100) silicon wafer. Onto the etched wafer a 1–2 μm thin P(VDF/TrFE) film is formed by spin coating. The pyroelectric copolymer is electrically connected by evaporated electrodes. In this way, both single-element sensors and sensor arrays are produced. Single-element sensors built up from P(VDF/TrFE) with a VDF content of 70–80% on an SiO2/Si3N4 membrane achieve a specific detectivity of up to 3.5×108 cm √Hz W−1 at a modulation frequency of 10 Hz and are temperature stable up to at least 55 °C. For linear arrays noise-equivalent power (NEP) values of 4.5 and 12 nW have been measured at chopper frequencies of 40 and 128 Hz, respectively. The average voltage responsivity Rv (500 K) of P(VDF/TrFE) linear arrays is about 110 000 V W−1 at 40 Hz and 40 000 V W−1 at 128 Hz.

Application of P(VDF/TrFE) thin films in pyroelectric detectors

Abstract Copolymer thin films can be cast by coating a thickness of 0.8 μm to 2.5 μm on solid silicon substrates as well as on unrestrained 800 nm thin SiO2/Si3N4 supporting membranes. By poling the P(VDF/TrFE) at about 140 V/μm, a high spontaneous polarization can be obtained without any stretching process. Measurements of dielectric constant, dielectric losses and pyroelectric coefficient confirm the ideal nature of these materials for pyroelectric detectors. Built-up single element detectors distinguish themselves by a high specific detectivity D* of 2 · 108 cm√Hz/W at a frequency of 10 Hz.

PyI12: Pyroelectric single-element detectors and arrays based on modified TGS

Abstract Pyroelectric detectors based on modified triglycine sulphate are described. Single-element detectors reach D*(500 K, 10 Hz, 25 °C) values up to 2×109cm Hz1/2/W. Linear arrays (128 elements, 100 μm pitch) and two-dimensional arrays (128×128 elements, 50 μm pitch) with NEP (500 K, 40 Hz, 25 °C) values up to 1 nW (0.16 nW/ Hz1/2) and NEP (500 K, 10 Hz, 25 °C values of 0.4 nW respectively were also realized.

Modified triglycine sulphate for pyroelectric infrared detectors

Abstract Doped single crystals of the TGS family show very good pyroelectric and dielectric properties, which enable them to be applied in pyroelectric detectors. Single domain deuterated and 1-α-alanine doped TGS crystals (DTGS:L-A) and TGS crystals doped with a l-α-alanine/Cr3+ complex (TGS:L-A + Cr3+) were grown. By deuteration Curie temperature can be increased up to 61°C. To improve homogeneity of alanine incorporation and so the uniformity of the internal bias field, the DTGS:L-A crystals were grown at {001} plate seeds10 by the so called box method. TGS:L-A + Cr3+ have extremely high bias fields of more than 50 kV/cm. Thus a high pyroelectric effect is measured even at 100°C. As a result of extensive investigations low dielectric losses of about 2. 10-4… 1.10-3 at a frequency of 103 cps could be achieved with the doped modifications. Finally, the pyroelectric chips of single element, linear and two-dimensional arrays were described and the measured detector properties were summarised.

Pyroelectric sensors and arrays based on P(VDF/TRFE) copolymer films

Abstract The central problem of the sensor design is a good thermal insulation of the P(VDF/TrFE) thin film from the read-out circuit. Two variations were examined - thin carrier membranes of SiO2/Si3N4 produced through back etching and thick thermal insulating layers out of spin-coated polymers with via holes. Through simulation and measurements on single element sensors and linear arrays for both variants an optimal design could be established. Membrane sensors consisting of 1 μm P (VDF/TrFE) thin film deposited on a 0·65 μm thick membrane show within the frequency range of 10 Hz to 1 kHz comparatively higher values for responsivity and specific detectivity than insulating layer sensors. The insulating layer sensors have in the most favourable case a thermal cutoff frequency of about 100 Hz, below that the responsivity remains constant while the specific detectivity and NEP deteriorate again. The optimal layer thickness for the compound of BCB and P(VDF/TrFE) for a chopper frequency of about 100 Hz is a...

Infrared sensor based on the monolithic structure Si-P(VDF/TrFE)

Abstract This paper deals with thermal conditions of the sensing element and the signal processing of pyroelectric thin film sensors. A short description of the structure and operation of a pyroelectric sensor introduces the topic. By analyzing the complex normalized current responsivity TR (jω) and specific detectivity D*, an optimum sensor design was achieved. In the case of single-element sensors and linear arrays, the sensor consists of a self supporting carrier membrane of about 500 nm Si3N4 and 150 nm SiO2, made by back etching of silicone with a spin coated P(VDF/TrFE) film, with a thickness of 1–2 μm. In two dimensional arrays with high spatial resolution, a sandwich assembly would be preferred. Using a 10 μm thermal insulating layer with vias, the P(VDF/TrFE) layers optimum thickness comes to about 10 μm for chopper frequencies above SO Hz. Spin coating is a simple and reliable method to produce thin copolymer films. A high rate of β form polar crystallites can be obtained in the films confirmed...

Construction, properties and application of pyroelectric single-element detectors and 128-element CCD linear arrays

Abstract Pyroelectric detectors based on LiNbO 3 and L-alanine doped triglycine sulfate (DTGS:L-A) are described. Single-element detectors with ion-beam milled pyroelectric chips have D * (500 K, 10 Hz, 25 °C) values of 6 × 10 8 and 2 × 10 9 cm √Hz/W respectively. 128-element CCD linear arrays with NEP (500 K, 40 Hz, 25 °C) values of 4 and 1 nW respectively were also realized.

PYP214. Influence of surface layers and electrothermal coupling on dielectric loss of thin chips made from modified triglycine sulphate

Abstract Dielectric loss tanδ is an essential source of noise in pyroelectric detectors. In reflecting on the dielectric loss of thin chips made from modified triglycine sulphate (TGS), it has been found out and experimentally shown that surface effects and electrothermal coupling effects cause a considerable increase in dielectric loss. The publication gives data on temperature and frequency dependence of dielectric loss, depending on mounting, chip thickness, surface treatment regime, and electrode patterning technique.

Pyroelectric linear array IR detectors with CCD multiplexer

Responsive pyroelectric linear arrays are described. After a short representation of the principal detector function, the pyroelectric materials L-alanine doped triglycine sulfate (DTGS:L-A) and lithium niobate (LiNbO3) are characterized, and the system parts pyroelectric chip, CCD-multiplexer, and hybrid arrangement are described in detail. Finally, the measured properties responsivity, noise equivalent power, and modulation transfer function are summarized.