QUANTIHEAT EUROPEAN PROJECT Prototype Application Note

Prototype 8:

Ribbed Scanning Thermal Microscopy Probes

(KNT-SThM-2an) Lead Partner: Kelvin Nanotechnology Ltd, UK

These new SThM probes, based on the existing KNT product KNT-SThM-1an,

feature a standard probe base size and a structurally compensated cantilever to

give flatter cantilevers and minimise temperature induced cantilever bending.

They address a fundamental limitation of soft silicon nitride SThM probes: the

thermal bending of the cantilevers when approaching hot surfaces, which

ultimately causes the optical feedback to fail. The probes are able to stay in

contact with hotter surfaces, expanding the range of measurements and

samples that can be employed.

Key Benefits

Structurally compensated flat cantilevers.

High resolution thermal imaging at elevated cantilever temperatures.

Characterisation of polymer layers, semiconductor & electrical devices,

biological samples, and thin films.

Probe Specifications

Kelvin Nanotechnology provides batch fabricated thermal probes which provide better than 100 nm

resolution for both the topography and thermal images. Figure 1 below shows an optical image and

an SEM image of one of these probes.

P a g e 2 | 4

Figure 1: Optical image (left) of one of batch fabricated SThM-KNT-2an probe (left)) and SEM image of the entire cantilever

The cantilever is made of SiN with a thin metal wire deposited such that the highest resistance

portion of the wire is near the apex of the tip. The probe specifications are briefed in the table

below.

Probe base 1.5mm × 3.3mm Tip height ~ 10µm

Cantilever (Silicon Nitride)

150µm × 120µm × 0.35µm Current max 2.5mA DC (recommended)

Resistor metal 5nm NiCr + 40nm Pd Spring constant 0.40 N/m

Track and pad metal 5nm NiCr + 145nm Au Maximum Temperature 200 C

Resistance 275 – 425Ω (Typ 325Ω) Sensitivity App. 1Ω / deg C

Tip radius < 100 nm Series resistors (optional) 2 × 100 Ω (± 25 Ω)

Applications

Mapping of topography, temperature, and thermal conductivity of a

surface.

Samples with heating elements1 (thin metallic platinum wires) has been fabricated by e-beam

lithography on a silicon substrate which has a high thermal conductivity (Figure 2(a)). Lateral

heat spreading is limited and temperature abruptly drops outside the wires making it an ideal

candidate to measure the lateral resolution of the SThM probes.

A ribbed SThM probe (KNT-SThM-2an) has been employed in passive mode for measuring the

temperature distribution in the device when an electric current is injected. Figure 2(b)shows the

topography of the device and figure 2 (c) and figure 2 (d) shows the temperature measurement

of the heated element.

1 Device fabricated by École polytechnique fédérale de Lausanne (EPFL)

P a g e 3 | 4

Figure 2: (a) shows the device configuration of the heater device and (b) its topography obtained using the ribbed probes. (c)and (d) shows the temperature mapping obtained using the ribbed probes of the central heater when driven by 4mA and 13 mA respectively.

Detecting hot spots on surfaces

An example of a high temperature imaging using a 2nd generation probe is shown in Figure 3. Figure

3(a) shows the topographic image of a NiCr resistor element connected with gold pads. A high

current was passed through the NiCr and corresponding thermal image (Figure 3(b)) was measured

simultaneously. The hottest region of the resistor was measured at 108 C, demonstrating successful

scans at higher temperatures.

Figure 3:Topographic (a)and thermal image(b) of a NiCr heater device

Additionally, we have measured the thermal bend of the cantilever when heated with an external

heat source. Figure 4(left) shows a 3-D image of a second-generation probe obtained with an optical

interferometry when heated using an external heater. Bend is defined as the vertical displacement

of the free end of the cantilever from the probe base and Figure 4(right) plots the bending of the

cantilever at different probe temperatures ranging from 4 C to 130 C.

P a g e 4 | 4

Figure 4: 3-D image of a ribbed cantilever bending (left) obtained using the optical interfoermetry and the bend measured for different probe temperatures(right) when heated with an external heater

References http://web.eng.gla.ac.uk/groups/nano/afm/AfmPage.html

Contact details

Kelvin Nanotechnology Ltd.

web: www.kelvinnanotechnology.com

email: enquires@kelvinanotechnolgy.com

LinkedIn: www.linkedin.com/company/kelvin-nanotechnology-ltd