Characterization of room temperature metal microbolometers near the metal-insulator transition regime for scanning thermal microscopy

Abstract

Metal microbolometers, used in scanning thermal microscopy, were microfabricated from Ͻ20 nm titanium thin films on SiO 2 / Si 3 N 4 / SiO 2 cantilevers. These thin films are near the metal-insulator transition regime such that as the film thickness decreases-the resistance increases and the current-voltage characteristics cross over from sublinear to superlinear. In addition, the temperature coefficient of resistance transitions from positive to negative before it plateaus at a negative value. Thin titanium films exhibit negative temperature coefficient of resistance as high as −0.0067/ K which is higher than that of bulk titanium films. © 2009 American Institute of Physics. ͓doi:10.1063/1.3250434͔Uncooled microbolometers are currently used in the manufacture of highly specialized thermal imaging applications such as night vision and scanning thermal microscopy ͑SThM͒.1-3 In order to operate effectively, microbolometers must have a high temperature coefficient of resistance ͑TCR͒ and low noise characteristics. In addition, the materials used to manufacture microbolometers must be inexpensive and compatible with current complementary metal-oxidesemiconductor ͑CMOS͒ processes. These are the primary conditions that have to be met as part of the continuing effort to develop even smaller, better performing microbolometers that weigh less and consume less power.To date, various materials have been used to fabricate microbolometers. Polycrystalline and amorphous silicon have a high temperature coefficient of resistance ͑up to 0.05/ K͒ but exhibit adverse noise characteristics. [4][5][6] Vanadium oxide, on the other hand, has a TCR of approximately 0.05/ K and a superior noise equivalent temperature difference ͑NETD͒. However, vanadium oxide introduces a significant number of deposition problems.6-8 Thin film metallic microbolometers, in contrast, have very low noise characteristics in addition to a low TCR ͑0.005/ K͒. 6,9 Two types of SThM microbolometers have shown considerable promise: Doped silicon microbolometers, with TCRs between 0.003 and 0.0056/ K that are integrated into single-crystal silicon cantilevers, 10,11 and metallic microbolometers with a TCR of around 0.0029/ K.12 Thin film metallic microbolometers have other important advantages as well, including simplified fabrication and a lower manufacturing cost. Metallic microbolometers also enable the use of alternative substrate materials ͑such as polymers͒, that tend to exhibit higher compliance properties and improved thermal isolation for better temperature resolution.The electrical properties of granular metals vary as the composition of a metal and nonmetal mixture changes. 13Metal deposition goes through four phases before it starts behaving like a bulk film: nucleation, island formation, formation of island networks, and formation of continuous ͑but porous͒ film.14-17 The first three phases are considered discontinuous. Typically, island films have negative TCRs while porous films have a positive TCR. 14,15,[18][19][20] However, the TCR for porous fi...

A probe with ultrathin film deflection sensor for scanning probe microscopy and material characterization

“…Metallic sensing elements also enable the use of alternative substrate materials (such as polymers), that tend to exhibit higher compliance properties and improved thermal isolation [19,20]. Metal film sensing elements with thickness larger than 10 nm typically have gauge factors of about 2 or smaller [12,13,20,22].…”

“…Compared with doped-silicon sensing elements, deposited metal film elements have important advantages including simplified fabrication, a lower manufacturing cost [19], and the capability to scale down to smaller dimensions while maintaining sensitivities [12]. Metallic sensing elements also enable the use of alternative substrate materials (such as polymers), that tend to exhibit higher compliance properties and improved thermal isolation [19,20].…”

A piezo-thermal probe for thermomechanical analysis

“…10 Thin film elements have other important advantages, including simplified fabrication and a lower manufacturing cost. 9 Metallic sensing elements also enable the use of alternative substrate materials (such as polymers), that tend to exhibit higher compliance properties and improved thermal isolation. 9 The probes described in this paper include a monolithic integration of a heating element (which can also be used for temperature sensing) and a deflection (or displacement) sensing element.…”

“…9 Metallic sensing elements also enable the use of alternative substrate materials (such as polymers), that tend to exhibit higher compliance properties and improved thermal isolation. 9 The probes described in this paper include a monolithic integration of a heating element (which can also be used for temperature sensing) and a deflection (or displacement) sensing element. Gold films of 10 nm thickness were deposited on a) Telephone: 734-913-2608.…”

“…8 Cantilever metal sensing elements typically range in thickness from 100 nm to 30 nm. 8 Metallic thin film sensing elements can have high temperature coefficients of resistance 9 and high gauge factors. 10 Thin film elements have other important advantages, including simplified fabrication and a lower manufacturing cost.…”