Application of polyimide sacrificial layers for the manufacturing of uncooled double-cantilever microbolometers
- PDF / 1,438,349 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 102 Downloads / 149 Views
0890-Y08-15.1
Application of polyimide sacrificial layers for the manufacturing of uncooled double-cantilever microbolometers Shusen Huang and Xin Zhang Laboratory for Microsystems Technology, Department of Manufacturing Engineering, Boston University, Boston, Massachusetts 02215, USA. ABSTRACT In this paper, a low-temperature surface micromachining module with two sacrificial layers of polyimide is developed for the manufacturing of double-cantilever microbolometer focal plane arrays. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. For the patterning of the polyimide, a plasma-enhanced chemical vapor deposited silicon oxide is employed as a mask layer. Anisotropic etching of both the mask film and the polyimide layer is accomplished by reactive ion etching. After patterning structural layers, sacrificial etching of the polyimide is conducted using an isotropic dry etch process in high-density oxygen plasma. INTRODUCTION Uncooled double-cantilever microbolometers have the potential of reaching a noise-equivalent temperature difference (NETD) approaching the theoretical limit and thus have gained increasing interest [1]. Fig. 1(a) gives the cross section of a pixel in such a microbolometer focal plane array (FPA), showing the major elements and materials; Fig. 1(b) shows the top-down view of a portion of an FPA. As shown in the figure, each pixel consists of two overlapping bimaterial cantilevers that deflect in opposite directions as their temperature rises due to absorption of incident infrared radiation. The micromechanical deflection can then be detected by measuring the change of the capacitance either between the bottom cantilever and the substrate or, between the two cantilevers. NiCr
Al
SiNx SiNx
Pt/Ti Substrate Al
(a)
SiO2
Pt/Ti
NiCr
Al
SiNx
(b)
Figure 1. (a) Cross section of a pixel showing the major elements and materials of double-cantilever microbolometers; (b) top-down view of a portion of an array.
0890-Y08-15.2
Theoretical prediction indicates that the sensitivity of a cantilever microbolometer is inversely proportional to the gap distance between the cantilever and its substrate [1]. A small gap will result in high performance; however a small gap also leads to severe stiction problems if wet etching is employed to release the micro cantilevers [2]. In this paper, we report the fabrication of the double-cantilever microbolometer FPAs using a surface micromachining module with polyimide as a sacrificial material. The use of spin-on polyimide allows not only an all-dry final release step overcoming stiction problems, but also complete compatibility with deposition and patterning of infrared structural layers, i.e., plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) and electron beam (e-beam) aluminum (Al) in this work. EXPERIMENTS Since the fabrication process of the microbolometer FPA needs to be IC-process compatible and the PECVD SiNx is deposited at 300 °C, a co
Data Loading...
