Design issues involved in the development of a membrane-based high-temperature nanocalorimeter A.F. Lopeandı ´a a , E. Leo ´ n-Gutierrez a , J. Rodrı ´guez-Viejo a, * , F.J. Mun ˜oz b a Grupo de Nanomateriales y Microsistemas, Departamento de Fı ´sica, Universidad Auto ` noma de Barcelona, 08193 Bellaterra, Spain b Instituto de Microelectro ´ nica de Barcelona-Centro Nacional de Microelectro ´ nica, Campus UAB, 08193 Bellaterra, Spain Available online 27 January 2007 Abstract In this contribution, we present a membrane-based nanocalorimeter that is capable of measuring the heat released or absorbed during a phase transformation in ultrathin films at temperatures up to 1300 K. Standard semiconductor processing techniques are used to fab- ricate the microreactors. Heating and sensing is typically performed using Pt(100 nm)/Ti(10 nm) thin films covered by 150 nm of Al 2 O 3 to ensure high-temperature electrical stability, a key point to perform reproducible nanocalorimetric measurements. The 180 nm SiN x membrane is mechanically stable for temperatures below 1250 K. We demonstrate the use of the scanning nanocalorimeter to measure solid-to-liquid transitions occurring in a 3 nm nc-Ge layer sandwiched between 10 nm SiO 2 thin films. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Membrane-based microsystems; High-temperature stability; Nanocalorimetry; Ge thin film 1. Introduction Due to their low thermal mass and small dimensions micromachined membrane-based devices offer significant advantages from the point of view of thermal management, sensing and power consumption over more traditional sys- tems. The possibility to achieve very fast heating/cooling rates makes them interesting as microreactors to run dan- gerous exothermic reactions [1] or as nanocalorimeters to measure phase transition in thin film systems [2]. Allen and co-workers have shown that at fast heating rates these microsystems behave quasi-adiabatically and therefore the heat capacity can be directly calculated from the input power. Typically, membrane-based calorimeters are used at low-to-medium temperatures [2,3] to reduce the adverse effect of heat losses and to benefit from their excellent thermo-mechanical properties in this temperature range. Extension to higher temperatures entails a detailed knowl- edge of the influence of design parameters on the function- ality and lifetime of the microdevice. In this paper, the requirements to withstand high temperatures during oper- ation are analyzed. A detailed description of the influence of heat losses on the calorimetric measurements will be fur- ther explored in a forthcoming paper. 2. Thin film nanocalorimeter Nanocalorimeters were fabricated at the clean room of the Instituto de Microelectro ´ nica de Barcelona (IMB- CNM) using standard microfabrication technologies [4]. Details of the microfabrication process and a schematic cross-section of the nanocalorimeters are shown in Fig. 1a–d. Briefly, the heater is patterned on top of a 180 nm SiN x layer deposited on a 4 in. Si wafer. Subse- quently, an alumina layer is added on top of the metallic heater by using appropriate masks and a lift-off process. Finally, a wet etching step is used to free the membrane. The new design of the nanocalorimeter is oriented towards achieving fast heating rates, with a flat temperature profile in the sensing area, up to temperatures in the vicinity of 0167-9317/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2007.01.054 * Corresponding author. Tel.: +34 93 5811769. E-mail address: Javier.Rodriguez@uab.es (J. Rodrı ´guez-Viejo). www.elsevier.com/locate/mee Microelectronic Engineering 84 (2007) 1288–1291