______________________________________________________________________________________________ ____ 1 st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine & Biology 1 October 12-14, 2000, Lyon, FRANCE Multisensor silicon needle for cardiac applications N.Zine (1), A. Ivorra (1), J.Aguilo (1), R. Villa (1), J. Millan (1), J.Bausells, Member, IEEE (1), A.Errachid (1), P. Godignon (1), A. Benvenuto (2), L. Beccai (2), F. Valvo (2), A. Menciassi (2), P. Dario (2), Member, IEEE and M.C. Carrozza (2) (1) Centre Nacional de Microlectrònica (IMB-CSIC), Campus UAB, 08193 Bellaterra (Barcelona), Spain. Tel 34 93 594 77 00, Fax 34 93 580 14 96, E-mail abdelhamid. errachid@cnm.es (2) Scuola Superiore Sant’Anna , Via Carducci 40, I-56127, Pisa, Italy Abstract – An integrated chemical sensor with multiple ion and temperature sensors, composed of two ISFETs (pH and K + ), one platinum pseudo-reference electrode and a temperature sensor based on a platinum resistor has been realised by using a CMOS-compatible technology and silicon micromachining. This paper describes a summary of the fabrication process and results of the device characterisation in vitro. The feasibility of the fabrication technology has been demonstrated and all devices have operated satisfactory, with a response showing good sensitivity and linearity. This multi-sensor will be used in the on-line early detection of myocardial ischemia during cardiac surgery while the heart is artificially arrested (extracorporeal circulation). I. INTRODUCTION One of the most prevalent causes of mortality in developed countries are cardiovascular diseases. Cardiac mortality has decreased due to advances in cardiac surgery, but some improvement are still required to reduce postperative deaths. Post-operative mortality in patients undergoing cardiac surgery is markedly related to the effectiveness of myocardial protective techniques applied during the operative phase of extracorporeal circulation. During this surgical period, the heart is artificially arrested and, therefore, the electrocardiogram (ECG) is not reliable to detect myocardial injury (ischemia). However, myocardial ischemia induces rapid alterations in whole tissue impedance [1] and in extracellular K + concentration and pH [2] which, in contrast to the ECG, can be adequately monitored in arrested hearts. Silicon technologies can be used to integrate different sensors in a small size device, which can be used for myocardial ischemia monitoring. In this work we present a multi-sensors silicon needle for the simultaneous measurement of K + and H + ions and temperature on the myocardial tissue. Ion measurements are based on ion- sensitive field-effect transistors (ISFET). Fig. 1 shows a schematic view of the device structure. In a companion paper [3], we report a similar device for impedance measurements. Pseudo-electrode Temperature sensor ISFET 500μm P-Si Fig.1: Outline of the device structure. II. FABRICATION PROCESS The devices have been fabricated on <100>-oriented, p-type silicon wafers with nominal resistivity of 4 to 40 Ω.cm, which corresponds to a doping level of 1x10 15 cm -3 . The fabrication process starts with the fabrication of the ISFET devices and includes a final micromachining step to define the silicon needles. Level ISFET Technology 1 Diffusion windows 2 Gate regions 3 Membrane definition 4 Contacts 5 Metal conductors 6 Passivation layer Table. 1: Summary of the mask steps used for the fabrication of Si 3 N 4 -gate ISFETs.