Porous Silicon Membranes over Cavity for Efficient Local Thermal Isolation in Si Thermal Sensors

Abstract

An improvement of porous silicon technology for local thermal isolation on bulk crystalline silicon is presented. The technique consists of forming an air cavity below the porous layer to increase the thermal isolation efficiency. Both porous silicon and the cavity underneath are formed during the same electrochemical process in two steps: in step 1 the current density used is below a critical value, and in step 2 it is switched to a value above the critical current for electropolishing. In this way, porous silicon is formed first, followed by the formation of the cavity underneath. Experimental results and simulations are shown together with an application of this process in a thermal silicon flow sensor.

Effect of Etching Time on Optical and Thermal Properties of p-Type Porous Silicon Prepared by Electrical Anodisation Method

“…Related to these applications, the ability of adjustment and control of some parameters are more important. The band gap and the thermal diffusivity are two important parameters in sensors, solar cells [15,16], electronic [17] and optoelectronic [18,19] devices, thermal flow sensors [20], isolators [21], and fuel cells [22,23]. In this study, we will study on the band gap and the thermal diffusivity of PSi samples prepared by electrical anodisation method in different etching time.…”

A novel thermal position sensor integrated on a plastic substrate

“…Typically Si-based MEMS devices suffer from a large amount of heat dissipation throughout their structure, due to the presence of the high thermal conductivity silicon substrate. In order to overcome this drawback various ways to achieve thermal isolation to the substrate have been reported, such as the use of vacuum cavities, porous silicon or suspended structures [9][10][11] but these are most often costly methods employing demanding process steps, while resulting to a high degree of surface anomaly which could impose limitations to further structure fabrication. In the present case, both the SU-8 and the FR4 materials present very low thermal conductivity values of the order of 0.2W/m·K this way enhancing the lateral sensitivity of the device.…”

Fabrication and testing of an integrated thermal flow sensor employing thermal isolation by a porous silicon membrane over an air cavity

“…The process flow for the improved porous silicon thermal isolation technology and the gas flow sensor are described elsewhere [8,9]. An outline will be presented in the following sections.…”

“…The successful fabrication of various integrated thermal sensors employing porous silicon thermal isolation technology has been reported in the literature [6][7][8]. An improvement of this technology has been recently developed by the authors [9], based on the creation of an air cavity underneath the porous membrane. The even lower thermal conductivity of air (2.62 × 10 −2 W m −1 K −1 ) compared to that of porous silicon assures a superior local thermal isolation on top of the porous membrane.…”