Short answer: Neither sensor is universally "better." Cernox® thin-film RTDs and DT-670 silicon diodes are both excellent cryogenic temperature sensors, but they solve different problems. Cernox dominates in magnetic fields, ionizing radiation, and sub-1 K work; silicon diodes win on price, interchangeability, and simple instrumentation across a wide 1.4 K to 500 K range. The "better" choice is the one whose strengths align with the constraints of your cryostat or experiment.
If you'd rather skip the comparison and see the full performance matrix, download the Lake Shore Temperature Sensor Selection Guide.
Quick comparison: Cernox vs. silicon diodes
| Attribute | Cernox® (CX) | DT-670 Silicon Diode |
|---|---|---|
| Useful temperature range | 100 mK – 420 K (model dependent) | 1.4 K – 500 K |
| Sensor physics | Negative temperature coefficient thin-film RTD | Forward voltage drop across a p-n junction |
| Standard curve / interchangeability | No — individual calibration recommended | Yes — conforms to Curve DT-670 |
| Magnetic field performance | Excellent above ~1 K; very low magnetoresistance | Fair only above ~60 K; orientation-dependent offsets |
| Ionizing radiation tolerance | Excellent (typical errors <25 mK at 1 Mrad) | Poor — errors of 0.5 to 2 K at similar dose |
| Thermal response time | 1.5 ms at 4.2 K (bare die) | Among the fastest of any silicon diode (DT-670E-BR) |
| Typical excitation | ≤10 mV (AC resistance bridge) | 10 µA constant current |
| Best for | High-field magnets, radiation environments, dilution refrigerators, UHV | General cryogenic monitoring, cryocoolers, cold heads, shields |
| Relative price | Higher | Lower |
What is a Cernox sensor, and when is it the right choice?
Cernox® sensors are zirconium-oxy-nitride thin-film resistance temperature detectors deposited on a sapphire substrate. The result is a small, fast, rugged cryogenic RTD with a smooth, monotonic resistance-vs-temperature response from 100 mK up to 420 K, depending on model.
Three characteristics make Cernox the default choice for demanding low-temperature thermometry:
- Low magnetoresistance. Magnetic-field-induced errors are typically negligible above 30 K and remain small at low temperatures, with no strong orientation dependence — critical inside superconducting magnets, MRI bores, and high-field cryostats.
- Radiation hardness. Cernox sensors hold calibration after Mrad-level exposure, making them the standard for space missions, particle accelerators (e.g., the LHC), and fusion R&D.
- Fast thermal response. Bare-die Cernox responds in ~1.5 ms at 4.2 K and ~50 ms at 77 K, useful for dynamic cooldown measurements and fast PID control loops.
The trade-off: Cernox does not follow a standard curve, so each sensor needs an individual calibration for best accuracy, and the cost-per-channel is higher than a diode. The CX-1010 model can replace germanium RTDs down to 100 mK while still operating to room temperature, which is unique in the industry.
Explore the models. See resistance curves, packaging options (SD, AA, BC, BG, BR, CU/CU-HT), and calibration ranges on the Cernox product page.
What is a silicon diode sensor, and when is it the right choice?
Silicon diode thermometry exploits the temperature dependence of the forward voltage drop across a p-n junction biased at a constant 10 µA current. Because the signal is large (roughly 0.1 V to 6 V) and follows a well-defined standard curve, diodes are easy to read out and easy to swap.
Lake Shore's DT-670 Series silicon diodes are the workhorse of cryogenic instrumentation:
- Wide range, one curve. A single curve DT-670 covers 1.4 K to 500 K, and sensors within a tolerance band are interchangeable without re-calibrating the instrument.
- Simple instrumentation. Constant-current excitation plus a voltage reading — no AC resistance bridge required, which keeps both sensor and controller cost down.
- Multiple form factors. From the rugged SD package to the bare-die DT-670E-BR (the smallest, fastest silicon diode on the market) and the flat-substrate DT-621-HR for surface mounting.
Where diodes fall short: silicon diodes are not recommended in magnetic fields or ionizing-radiation environments, and they cannot read below 1.4 K. Their sensitivity also drops above ~30 K (the curve flattens to roughly −2.1 mV/K), so for high-precision work above room temperature a platinum RTD is usually a better match.
Pro tip — Match your sensor to your controller. Most Lake Shore temperature controllers and monitors read both Cernox and DT-670 natively, so you can mix sensor types on different stages of the same cryostat — diodes on the cold head and warm stages, Cernox on the sample and magnet-adjacent points.
How to decide: a 4-question shortcut
When researchers ask us "Cernox or silicon diode?" the answer almost always falls out of four questions:
- Will the sensor sit in a magnetic field? If yes — even a few tesla — choose Cernox. Silicon diode magnetoresistance and orientation offsets will dominate your uncertainty budget.
- Will the sensor see ionizing radiation (space, accelerator, fusion, neutron beamline)? Choose Cernox. Diode p-n junctions degrade quickly under dose.
- Do you need to measure below 1.4 K (dilution fridge, ADR, He-3 system)? Choose Cernox (or, below ~50 mK, look at Rox™ and germanium options).
- Is this a general-purpose cryostat, cryocooler stage, shield, or cold plate from 1.4 K to 500 K, with no field and no radiation? A DT-670 silicon diode is almost always the most cost-effective answer, especially when you want interchangeability without per-sensor calibration.
Application cheat-sheet
- Superconducting magnet systems, MRI, NMR cryostats → Cernox
- Dilution refrigerator mixing chamber and still → Cernox (CX-1010, CX-1030)
- Quantum computing dilution-fridge stages with magnetic shielding → Cernox
- Cryocooler cold head temperature monitoring → DT-670 silicon diode
- Liquid-helium and liquid-nitrogen Dewar instrumentation → DT-670 silicon diode
- Space-flight thermometry, accelerator beamlines, tokamak diagnostics → Cernox (often the HR Series for spaceflight)
- General cryostat cooldown verification, shields and radiation baffles → DT-670 silicon diode
Frequently asked questions
Is a Cernox sensor more accurate than a silicon diode? For a calibrated Cernox at cryogenic temperatures, yes, particularly below 30 K and in magnetic fields. Above ~100 K, the accuracy gap narrows significantly, and silicon diodes can be more than adequate for typical lab work.
Can I use the same instrument to read both? Yes. Lake Shore controllers and monitors (e.g., Model 336, Model 350, Model 224) accept both diode and resistance inputs and can mix them across channels.
Why is Cernox more expensive? Cernox is fabricated in-house using a proprietary thin-film process on sapphire wafers and is typically calibrated individually against NIST-, NPL-, and PTB-referenced standards. Silicon diodes leverage a standardized curve and don't require per-unit calibration for most uses.
What about temperatures above 500 K? Neither sensor is the right tool. Look at platinum RTDs (to 873 K) or thermocouples.
Still not sure? Talk to a cryogenic thermometry specialist.
Choosing the right cryogenic temperature sensor is a balance of physics, packaging, and budget. If you'd like a second set of eyes on your application — magnet geometry, vacuum compatibility, radiation environment, calibration needs — our applications engineers are happy to help.
Contact Lake Shore Cryotronics for a sensor recommendation tailored to your experiment or download the Temperature Sensor Selection Guide to compare all Lake Shore sensor families side-by-side.