Heiko Thust

Using LTCC for microsystems

A characteristic feature of LTCC is good workability. In some cases a LTCC‐based microsystem can be a good alternative to microsystems made in silicon or other technologies. Reasons for choosing LTCC‐Technology may be financial considerations or specific material properties. A main problem is to simplify a mechanical component in such a way, that it is possible to integrate this component in a planar structure with a small height in consideration of the restrictions of the LTCC‐Technology. In contrast to LTCC‐based substrates with only electrical circuits the integration of mechanical components make other demands on the different technological steps of the LTCC‐Process. In this paper some 3D‐structures made in LTCC‐like fluidic channels, membranes usable for micropumps or pressure sensors – and some aspects of required special technological demands are described.

Technology Benchmarking of High Resolution Structures on LTCC for Microwave Circuits

Low temperature co-fired ceramics (LTCC) is being widely used for microwave circuits. The BMBF funded R&D-project KERAMIS focuses on larger implementation of functionality in LTCC substrates to allow designs with standard MMICs. Target applications are circuits for multimedia satellite communications. In order to add more functionality in LTCC, current patterning limits of line width and line separation (100 mum) need to be extended. Four different technologies are considered candidates for higher resolution: a) fine line printing technology with special screens, b) photo-imageable pastes, c) etching of thick film conductors (co- and post-fired) and d) thin films on LTCC. For this purpose, a test coupon was designed and manufactured by the consortium members. The artwork contains lines, line transitions, ring resonators (microstrip and stripline), edge-coupled filters, DC blocking structures, and various lines for DC resistance testing. The smallest gap definition is 50 mum. Two substrate materials, Du Pont tape 951 and 943, are included in the study. Besides the main frequency band of interest in the project (17-22 GHz), these structures have been characterised up to 50 GHz. Electrical results are correlated to physical measurements of the features (line width, spaces and tolerances). Data are evaluated with respect to performance, manufacturability, and yield

Electrical and stability properties and ultrasonic microscope characterisation of low temperature co-fired ceramics resistors

Abstract This paper presents systematic investigations of electrical and stability properties of various low temperature co-fired ceramics (LTCC) resistors. One of the goals of this work was to check the compatibility of LTCC materials (tapes, resistive and conductive inks) from various manufacturers. Three commercially available green tapes and three LTCC resistor/conductor systems were examined. The resistive inks with 1 k Ω/ sq . nominal sheet resistance were used. Buried (inside) and surface resistors were laminated and fired according to the tape manufacturers’ recommendations. The influence of dimensional effect on sheet resistance and hot temperature coefficient of resistance, the temperature dependence of resistance in a wide temperature range (from −180°C to +130°C), long-term stability of thermally aged as-fired resistors (150°C, 500 h) and durability to high-voltage micro- or nanosecond pulses (50 ns pulses with 4000 V/mm maximum electric field or 10 μs ones with 700–1000 V/mm electrical field) were carried out for electrical and stability characterisation of LTCC resistors. Non-destructive scanning acoustic microscope diagnostics was applied for structure investigation and estimation of lamination and cofiring process quality of buried LTCC resistors.

Heat transfer enhancement at solid-liquid and solid-gas interfaces by near-surface coolant agitation

Heat transfer enhancement from glass ceramic plate to water or air by agitation of the coolant near the heated surface was investigated. The experimental arrangement consisted of a ceramic plate of dimensions of 47/spl times/35/spl times/0.26 mm/sup 3/, attached to a brass vessel with inner dimensions of 34/spl times/30/spl times/4 mm/sup 3/. The ceramic plate was provided with a 5/spl times/5 mm/sup 2/ size printed heater on the opposite side from the vessel. The temperature field across the plate was recorded by an infra-red camera. The agitation of the coolant in the vessel (air or water) was performed by a vibrating piezoelectric beam of dimensions of 26.5/spl times/12/spl times/0.6 mm/sup 3/, fixed at 1 mm distance from the heated plate, or alternatively by a magnetic rod of diameter of 2.2 mm and length of 15 mm. The vibration of the beam with amplitude of some tenths of mm peak to peak at frequencies of 200 to 400 Hz caused the sinking of the peak temperature of the heater from about 90/spl deg/C to 45/spl deg/C in case of water as the coolant and from about 110/spl deg/C to 100/spl deg/C in the air. The magnetic rod, rotating in water at speed of some rounds per second lowered the heaters peak temperature from 85/spl deg/C to 50 to 60/spl deg/C. The ambient temperature in all experiments was 22 to 25/spl deg/C and the heating power 1-2 W. The power needed for agitation was about 50 mW in case of piezoelectric vibrator and about 1 W in case of the rotating agitator drived by a fan. Using numerical simulation by ANSYS, it was demonstrated, that the temperature distribution across the plate with heater can be satisfactorily simulated using a two-dimensional (2-D) model with appropriately enhanced heat conductivity of the plate and heat transfer coefficient from the plate. For the experimental arrangement used the equivalent heat conductivity of the ceramic plate in case of agitated liquid cooling was up to 150 W/m/spl middot/K and heat transfer rate up to 300 W/m/sup 2//spl middot/K.

Progress in the Integration of planar and 3D Coils on LTCC by using photoimageable Inks

This paper presents some results of our investigations in the integration of coils in LTCC using the Fodel® Technology as line patterning technology. Planar as well as 3-D inductors were simulated, manufactured, measured and modeled. The structures were manufactured with different shapes, a line width from 30 μm to 70 μm, a space between turns from 100 μm and 200 μm and diameters of inner turns from 0.5 mm to 2 mm. The smallest and most critical inductors (0.5 mm diameter) were manufactured with vias, whose diameter were about 60 μm. The manufacturing of smaller coils was possible due to the increased resolution of Fodel® thick-film inks also in inner layers in combination with micro vias, which were produced with a multifunctional Laser. Combining these technologies with buried cavities and a symmetric turn arrangement we obtained inductors that can be used in a wider range of frequencies (up to 10 GHz).

Laser Forming of LTCC ceramics for Hot-Plate Gas Sensors

Hot-plate LTCC gas sensors combine advantages of silicon structures (low power consumption) and typical ceramics gas sensors (stability and reliability). Such elements can be integrated in MEMS packages as well as in ceramic sensor arrays. Moreover, they can be produced in small series with relatively low cost. One important key in hot-plate design are properly formed beams. This paper presents possibilities and problems related to laser forming of LTCC ceramics for hot-plate gas sensors. Influence of beam width on power consumption and temperature distribution is discussed. Possibilities to achieve beam width as narrow as possible are practically tested by laser cutting. Obtained results are very promising for future work and for possible application of LTCC ceramics in such type of gas sensors.

Electrical Properties of Low Temperature Cofired Ceramics with Integrated Bulk Metals

Constrained sintering allows the cofired integration of bulk metals in LTCC (low temperature cofired ceramics) instead of paste prints. A difficulty of such an integration is the application of the metallic structures on the sensitive unfired ceramic foils. The paper shows different techniques for solving this problem. Higher possible resolution and more precise edges are the advantages of bulk metal structures. Other results are improved electrical properties. Different kinds of conductor designs were used to figure out the electrical features in the fields of radio frequencies and high power applications. The reduction of transmission losses in triplate lines up to frequencies of 45 GHz will be shown and discussed. Coils for powers supplies were investigated and measured at lower frequencies. Higher specific conductivity and thickness of bulk lines allow the realization of inductors with higher quality factor and lower resistance. The advantages of the new cofiring technology for LTCC and the potential for different applications will be discussed.